Type Species:

Cibolaites molenaari Cobban and Hook, 1983: 16, pl. 2, figs. 1–9; pl. 3, figs. 3–8; pl. 8, figs. 6–8; pl. 13, figs. 1–5; pl. 14; text-figs. 13, 14; lower Turonian Mammites nodosoides Zone, west-central New Mexico.

Diagnosis:

A medium-size genus, largest known adults 120 mm in diameter; dimorphism not demonstrated. Coiling involute with small umbilicus, whorl section compressed to depressed, intercostal section with convergent sides and fastigiate venter, costal section markedly concave between tubercles. Strong conical umbilical bullae give rise to primary ribs singly or in pairs with shorter, intercalated ribs, all with ventrolateral and siphonal clavi on phragmocone. Umbilical bullae decline on the adult body chamber, which is flat-sided with crowded weak primary and intercalated ribs; ventrolateral and siphonal tubercles decline progressively and the venter flattens towards the adult aperture.

Suture relatively simple with broad, little-divided saddles and narrower, rectangular lobes.

Discussion:

Coarse tuberculation and presence of only a single row of ventrolateral tubercles distinguishes Cibolaites from all other genera currently referred to the Collignoniceratinae. Cibolaites superficially resembles Barroisiceras de Grossouvre, 1894, and Subbarroisiceras Basse, 1946, of the upper Turonian–Coniacian Barroisiceratinae. However, they differ in sutural characteristics, while both are more involute than Cibolaites, with smaller umbilici and crenulate keels; in Cibolaites there is no continuous keel and the siphonal clavi are separated by smooth interspaces.

Occurrence:

Upper Cenomanian Neocardioceras juddii Zone in Devon, England and Aube, France; lower Turonian Mammites nodosoides Zone, immediately below first appearance of C. woollgari woollgari of the middle Turonian in west-central New Mexico; M. nodosoides Zone, N.W. Germany; also recorded from northern Spain (Kaplan, 1988) and from Tunisia (Chancellor et al., 1994).

Types:

Holotype is USNM 328766 (fig. 5), from the Rio Salado Tongue of the Mancos Shale, lower Turonian Mammites nodosoides Zone, immediately below the first occurrence of Collignoniceras woollgari woollgari of the middle Turonian at USGS Mesozoic locality D11208, NE1/4 sec. 36, T. 6 N, R. 19 W, Cibola County, New Mexico. Paratypes USNM 328752–328767, 329013, are from the Rio Salado Tongue at this and nearby localities.

Diagnosis:

Characteristic features of this moderate-size species are the strong, nodate umbilical tubercles during early and middle growth and the equal numbers of prominent siphonal clavi and clavate inner ventrolateral tubercles.

Description:

The early whorls are smooth to a diameter of 5 mm, with rounded flanks and venter. Low umbilical bullae, 14 per whorl, appear between 5 and 7 mm diameter; ventrolateral and siphonal tubercles appear around 10 mm diameter. As size increases (figs. 6, 7), the number of bullae decreases to as few as seven per whorl in middle growth. Coiling is fairly involute, with a deep umbilicus. Two broad prorsiradiate to rectiradiate ribs generally arise from each bulla, which vary in strength within and between specimens. The ribs are broad, rounded, and terminate in strong ventrolateral clavi; occasional intercalated ribs arise around midflank or below and bear clavi of comparable strength to give a total of 22 or so ribs per whorl at diameters of up to 65 mm. Each ventrolateral clavus gives rise to a broad, low prorsiradiate rib that arches forward across the venter to form an obtuse chevron with a strong siphonal clavus at the apex. In profile, the adapical slope of this clavus is low, the adapertural slope much steeper, giving the clavus a distinctly asymmetric profile. At this stage the costal and intercostal whorl sections vary from compressed to depressed (see table 1); the greatest breadth in intercostal section is just outside the umbilical shoulder. The inner flanks are broadly rounded, the outer flanks flattened and convergent, and the venter fastigiate. The costal section has the greatest breadth at the umbilical bullae and the flanks are concave between tubercles; the venter is markedly fastigiate. On the later parts of the phragmocone as well as on the adult body chamber, the ornament is progressively modified (fig. 5); first, the umbilical bullae decline and ultimately disappear. The ventrolateral and siphonal clavi weaken markedly, but are still present, though very weak, immediately adapical of the adult aperture. As they decline, the venter broadens and rounds. On the body chamber, the flanks flatten and the whorl section becomes rectangular, with low, weak, prorsiradiate ribs, irregularly long and short, the latter of variable length. Part or all of the body chamber is preserved on 46 specimens. Diameter at the last septum ranges from 44 to 94 mm, without any clear clustering into size classes or indication of size dimorphism. Suture with broad, bifid E/L, narrow, bifid L, slightly broader L/U₂, and much narrower U₂ (fig. 8).

Cibolaites molenaari occurs as gracile and robust forms, as indicated in the figure captions, although the distinctions between them are not as pronounced as in species of Collignoniceras and Prionocyclus. The holotype and paratypes figured by Cobban and >Hook (1983) can be assigned to the following forms: gracile form, pl. 2, figs. 1–6, pl. 3, figs. 3, 4, 6–8, pl. 14, figs. 1–15; robust form, pl. 2, figs. 7–9, pl. 3, fig. 5, pl. 8, figs. 6–8, pl. 13, figs. 1–5.

Discussion:

Coarse ornament and presence of only a single row of ventrolateral tubercles at all stages distinguishes C. molenaari from all of the collignoniceratids described here. Body chamber characters separate it from Lecointriceras fleuriausianum (D'Orbigny, 1841) (fig. 9) as discussed above.

Occurrence:

Upper Cenomanian Neocardioceras juddii Zone in Devon, England, and Aube, France; lower Turonian Mammites nodosoides Zone in west-central New Mexico and northeastern Arizona; N.W. Germany.

Type Species:

Ammonites woollgari Mantell, 1822: 197, pl. 21, fig. 16; pl. 22, fig. 7, by the original designation of Meek, 1876a: 453, as type species of Prionotropis Meek, 1876a (non Fieber, 1853) for which Breistroffer (1947, unpaged) proposed Collignoniceras as nomen novum, from the Turonian of England.

Diagnosis:

“Medium-sized, moderately involute to evolute ammonites. Early whorls compressed, parallel-sided, ornamented by crowded or sparse, prorsiradiate, straight or flexuous ribs, mostly long, with weak to strong umbilical bullae. All ribs bear in the early stages outer ventrolateral tubercles in addition to siphonal clavi. This style of ornament is, in some species, retained to maturity. In most, however, the ribs coarsen, become widely spaced, with strong to weak umbilical tubercles (which migrate progressively outward from the umbilical margin), prominent inner and outer ventrolateral tubercles, which may fuse into a massive horn or flared rib, from which commonly arise pairs of low ribs joining siphonal clavi more numerous than the ventrolateral and linked into a more or less continuous keel. Rarely the ornament is greatly reduced on the body whorl. Sutures little incised, with massive saddles” (Wright and Kennedy, 1981: 102).

Discussion:

See Kennedy et al. (1980: 558) and Wright and Kennedy (1981: 102).

Occurrence:

Middle to lower upper Turonian, England, France, Germany, Czech Republic, Poland, Roumania, eastwards to Turkmenistan, Japan, California, northern Mexico, the U.S. and Canadian Interiors, Greenland, North Africa, Colombia, south India, northern Australia.

Types:

Lectotype (fig. 10) is BMNH 5682, the original of Mantell, 1822: pl. 21, fig. 16, from the Middle Chalk of Lewes, Sussex, England; designated by Wright and Wright, 1951: 35. Presumed paralectotypes (fig. 27E, F) are BMNH C5742a, b, from the same locality.

Diagnosis:

This moderately evolute subspecies has prorsiradiate to rectiradiate primary and secondary ribs that support bullate inner ventrolateral tubercles and clavate outer ventrolateral tubercles matched by siphonal clavi.

Discussion:

Cobban and Hook (1979) provided an account of C. woollgari woollgari from New Mexico, and Kennedy et al. (1980) and Wright and Kennedy (1981) reviewed the European material at length. We illustrate here a selection of European, Mexican, and U.S. Western Interior material (figs. 10–15) for comparison with C. woollgari regulare, described below, where features distinguishing it from the nominate subspecies are outlined. Gracile and robust forms of C. woollgari woollgari are present, as indicated in the figure captions. Specimens figured by Cobban and Hook (1979) include gracile forms (pl. 1, figs. 1–3, 10, 11; pl. 2, figs. 5–19; pl. 5, figs. 13–16), and robust forms (pl. 1, figs. 4–9; pl. 2, figs. 20–22; pl. 4, figs. 11, 12; pl. 12, figs. 1, 2).

Occurrence:

Collignoniceras woollgari woollgari Subzone, widespread in the U.S. Western Interior from Wyoming to the Rio Grande; California, northern Mexico, Europe, east to Turkmenistan; Tunisia, Japan, and northern Australia.

Types:

Holotype, by original designation, South Dakota State School of Mines Collection no. 1470, the original of Haas, 1946, plate 16, figures 14, 16; text-figs. 80, 81, from an unknown horizon and locality in the Black Hills area (fide Haas, 1946: 198).

Material:

The present description is based on more than 500 specimens from USGS Mesozoic locality 21792, limestone concretions 18.9–21.3 m above the base of the Carlile Shale, middle Turonian Collignoniceras woollgari Zone, regulare Subzone, 1.6 km west of Newcastle in the NW¼ sec. 31, T. 45 N, R. 61 W, Weston County, Wyoming, and from USGS Mesozoic locality D9896, limestone concretions about 18.3 m below the Turner Sandy Member of the Carlile Shale, middle Turonian Collignoniceras woollgari Zone, regulare Subzone, NW¼ sec. 35, T. 46 N, R. 63 W, Weston County, Wyoming. We have several hundred additional specimens from many localities in South Dakota, Wyoming, Colorado, Utah, and New Mexico.

Diagnosis:

A moderately evolute subspecies that usually has prorsiradiate single ribs that support umbilical and inner and outer ventrolateral tubercles matched by prominent siphonal clavi.

Description:

Nuclei are highly variable (figs. 17, 21). At one extreme are compressed, high-whorled individuals of the gracile form (fig. 17A–C, J, K, O–Q, T, U, X, Y) with costal whorl breadth to height ratios of as little as 0.51 and an umbilical to shell diameter ratio of 0.29 (table 2). The umbilicus is broad, with a low umbilical wall, and a broadly rounded umbilical shoulder. The flanks are flattened and subparallel with the ventrolateral shoulders rounded. At diameters up to a maximum of 27 mm, there are dense, crowded ribs that total as many as 70 per whorl. They arise singly or in pairs at the umbilical shoulder or intercalate, arising at various levels just outside the umbilical shoulder and well below midflank. The ribs are straight, narrow and rounded, and prorsiradiate to the ventrolateral shoulder, where they flex forward; they are concave over the shoulder and project forward to the siphonal keel, producing an acute chevron. Small outer ventrolateral clavi are present from the earliest ornamented stage, and are separated by a ventral groove from the siphonal keel, which bears small clavi, equal in number to but displaced slightly aperturally of the outer ventrolateral clavi. Weaker inner ventrolateral clavi appear after the outer ones, and may be absent to a diameter of as much as 12 mm.

At the other extreme are more robust nuclei (fig. 21C, D, J–L) with whorl breadth to height ratios of up to 0.95 and an umbilical to shell diameter ratio of up to 0.40 (table 2). These have as few as 24 ribs per whorl, all of which are coarse, blunt, straight and prorsiradiate. The ribs bear weak umbilical bullae and prominent conical inner ventrolateral and clavate outer ventrolateral tubercles from an early stage. The siphonal keel is coarse.

There is every intermediate between these two forms in terms of rib density, and great variation in the diameter to which the simply ornamented stage persists. Thus, at a diameter of as little as 7 mm (fig. 21M–O) to a diameter of up to 27 mm there is a marked change in rib density; compressed gracile individuals may have as few as 17 or 18 ribs per whorl at diameters of 20–35 mm (fig. 21X–Z), decreasing to as few as 11 by a diameter of 75 mm (fig. 21U–W). The coiling in these gracile specimens is very evolute, with U/D up to 0.38 and intercostal whorl breadth to height ratios of as little as 0.57 (table 2). The umbilicus is very shallow, with a low umbilical wall, and rounded umbilical shoulder. The flanks are flattened and subparallel in intercostal section with rounded ventrolateral shoulders, and a high, sharp keel. The ribs are very narrow, and the interspaces between them become progressively wider as the diameter increases. At small diameters, the ribs originate at umbilical bullae, but with increasing diameter, the ribs become very high and flared, reaching their maximum elevation across the flanks. The ribs are markedly prorsiradiate, straight, and feebly concave across the flanks, and each rib bears a strong conical inner ventrolateral tubercle and a strong clavate outer ventrolateral tubercle. The two tubercles progressively assimilate into a flared ventrolateral rib that sweeps forward over the ventrolateral shoulder before weakening abruptly prior to meeting the siphonal keel. The keel is high and crenulate, with long, high, siphonal clavi that are markedly asymmetric in profile (fig. 23A–E). Fine lirae are developed, or not, on the interspaces between ribs (fig. 23), but do not bear any tubercles. There are an equal number of umbilical bullae, inner and outer ventrolateral, and siphonal tubercles. The largest individual of the gracile type from the Carlile Shale concretions has a diameter of 105 mm; fragments have whorl heights of up to 150 mm.

Robust variants show a comparable change in ribbing density at variable diameters. At diameters of up to 75 mm, these specimens have umbilical to shell diameter ratios of up to 0.34 and a quadrate whorl section. Ribs number as few as 14 per whorl with strong, persistent umbilical bullae. Ribs are blunt, low, coarse, and prorsiradiate, and bear large, conical inner ventrolateral tubercles that are connected by broad prorsiradiate ribs to strong, outer ventrolateral clavi. The siphonal keel is coarse with clavi that correspond in number to that of the outer ventrolateral clavi. The largest observed individual of the robust type is USNM 252804, 145 mm in diameter (Cobban and Hook, 1979; pl. 3, figs. 13, 14). Other fragments are still septate at 65 mm whorl height.

The collections also contain fragments of body chambers that show distant ribs with bullae that have migrated out to an inner flank position, and enlargement of the inner ventrolateral tubercles into long, finger-like horns (fig. 20B–D), into which the outer ventrolateral clavi are progressively assimilated. The mature body chamber morphology of the gracile form is best shown by specimens from the Chispa Summit Formation at Chispa Summit in Jeff Davis County, Trans-Pecos Texas. Here, compressed adult body chambers (Kennedy et al., 1989: fig. 23) that overlap in size and ornament with the similarly compressed juveniles from the Carlile Shale of Wyoming already described reach diameters of up to 200 mm. The intercostal whorl section is compressed oval. Distant ribs bear flared umbilical bullae, which progressively migrate out from the umbilical shoulder; each ventrolateral horn is linked by a high rib to a siphonal clavus. The costal whorl section is markedly fastigiate and a low siphonal ridge links the clavi. The final portion of the body chamber before the adult aperture is smooth and tubular without major ribs, but sometimes bears nontuberculate lirae. We tentatively interpret these forms as adult microconchs.

Much larger body chambers (figs. 24, 25) belong to the robust form. A South Dakota example is shown in fig. 25; at Chispa Summit, such specimens (fig. 24) are up to 360 mm in diameter. These correspond to the robust juveniles in the South Dakota fauna and we tentatively interpret them as macroconchs. In some there is a long, low siphonal clavus corresponding to each ventrolateral horn, successive clavi being linked by a siphonal ridge. Low riblets arise from the adapical and adapertural terminations of each ventrolateral horn and loop to the siphonal clavus. In others, small siphonal clavi may be present in the interspaces between larger ones.

European specimens referred to C. woollgari regulare (figs. 26–32) reach comparable sizes and show the same ontogenetic changes as the U.S. material described here.

Sutures moderately incised with broad, bifid E/L, narrower L, and L/U₂ broader than U₂ (fig. 33). Several sutures were illustrated by Meek (1876a: pl. 7, fig. 1e, h) and Matsumoto (1965: fig. 6A, D, F).

Discussion:

Gracile microconchs and robust macroconchs can be recognized from an early ontogenetic stage; the former dominate the Black Hills assemblages upon which the above description is largely based. Haas (1946) analyzed variation in C. woollgari, in large part on the basis of 325 specimens from a single concretion he believed to have been collected by the Powell Survey from southern Utah. We have never seen such concretion preservation from Utah and suspect rather that the material is from the Black Hills. Haas's Forma typica (1946: pl. 13, figs. 1, 4–19; text-figs. 3–5, 25–29, 31–38) are macroconch fragments; the original of his plate 14, figure 11, seems to be a crushed Plesiacanthoceras wyomingense Reagan, 1924. Variety regularis, the name selected for the late subspecies of woollgari (Haas, 1946: 154, pl. 16, figs. 1–17; text-figs. 10–12, 59–74, 78, 80, 81, 83), is based on gracile juvenile microconchs. Variety crassa (Haas, 1946: 153, pl. 14, figs. 1, 5; pl. 15, figs. 7, 8; text-figs. 6, 39) is based on evolute, robust, juvenile microconchs. Variety intermedia (Haas: 1946: 154, pl. 14, figs. 2–4, 6–10, 12–16; pl. 15, figs. 1–6, 9, 10; text-figs. 7–9, 40–44, 46–58) and variety tenuicostata (Haas, 1946: 155, pl. 16, figs. 18–21; text-figs. 13, 14, 75–77, 82) are based on juvenile microconchs.

C. woollgari var. praecox of Haas (1946: 155, pl. 16; figs. 2–33: pl. 17, figs. 1–5; pl. 18, figs. 1, 8, 9; text-figs. 15–18, 79, 84–90) is based on specimens from USGS localities 12642 and 18872 in the Black Hills of South Dakota, and Haas specifically noted that the variety is unknown from any other locality in the Black Hills area or in the block from “southern Utah” that yielded specimens of his other varieties. As already noted, subsequent collecting shows that this form, here regarded as a fully separate species (C. praecox), is younger than C. woollgari regulare. Collignoniceras praecox differs in the marked differentiation of ribs into strong and bullate and weak and nonbullate in the earliest stages of development, persistence of differentiated ribbing through middle growth, and the development in the adult of inner ventrolateral bullae or spines on distant primary ribs, many ventrolateral riblets, and an entire or minutely crenulate keel.

Matsumoto (1965: 11) also analyzed variation in juvenile Collignoniceras woollgari regulare from a collection made from 10 m above the base of the Carlile Shale 3.2 mi southwest of Newcastle, Wyoming. His groups A through D and F are probably all juvenile microconchs, his group E, juvenile macroconchs.

Collignoniceras woollgari regulare differs from the nominate subspecies in that in middle and later phragmocone whorls of the latter, there are more siphonal tubercles than ventrolateral ones, and looped ribs connect opposite ventrolateral horns. This generally also separates body chambers, but multiple siphonal tubercles sometimes appear on adult body chambers of C. woollgari regulare, as do looped ribs.

Collignoniceras vermilionense (Meek and Hayden, 1860) (see below) is a much smaller species, showing comparable dimorphism to that of C. woollgari regulare. Inner whorls are coarsely ribbed. In the microconch, which is adult at 55 mm diameter, coiling is very evolute. There are only outer ventrolateral clavi whereas in C. woollgari regulare of this size, there are both inner and outer ventrolateral clavi.

Occurrence: Widely distributed in the Western Interior of the United States from northern Montana south to Trans-Pecos Texas, and from central Utah east to western Iowa. It is also found in northeastern Texas as well as California and Oregon. The subspecies also occurs in Canada (Manitoba), northern Mexico (Chihuahua), southern England (figs. 27A–G) and France (figs. 26, 28–32).

Type:

Holotype by monotypy is USNM 224 (fig. 34D, E), from a limestone concretion in the Carlile Shale, inferred to be the middle Turonian Collignoniceras praecox Zone, on the Missouri River opposite the mouth of the Vermillion (formerly Vermilion) River in Dixon County, Nebraska.

Diagnosis:

A fairly small, keeled, evolute species that has closely spaced primary and secondary ribs on the innermost whorls, but mostly widely spaced, single, prorsiradiate ribs on later whorls. Ribs arise from low umbilical bullae and terminate in arcuate ventrolateral swellings that may or may not support inner ventrolateral tubercles and faint outer ventrolateral clavi. Keel is moderately high and strengthened into asymmetric clavi corresponding to the ribs.

Description:

The holotype is a juvenile. Coiling is very evolute, with U/D = 0.44–0.46 (table 3). The umbilicus is shallow, with a low, flattened wall and broadly rounded shoulder. The flanks are flattened. There are 26 primary ribs per whorl visible at a diameter of approximately 15 mm. All arise at the umbilical seam and strengthen across the umbilical shoulder. At the smallest observed diameter, there is a slight differentiation into stronger ribs with umbilical bullae separated by somewhat weaker ribs with weak or no bullae, but this differentiation declines and disappears with increasing size, and the ribs coarsen progressively. All ribs are blunt and recti- to feebly prorsiradiate on the flanks. Each rib strengthens into an inner ventrolateral bulla from which the rib projects strongly forward, declining markedly in strength and bearing a weak outer ventrolateral clavus.

USNM 299166 (Cobban, 1983: pl. 5, figs. 39, 40; fig. 34F, G), 56.0 mm in diameter, with inner whorls that are essentially identical to those of the holotype shows the succeeding ontogenetic stages. Coiling is very evolute, with U/D = 0.46 (table 3); the umbilicus is shallow, with a low wall. The intercostal whorl section is very compressed, with a whorl breadth to height ratio of 0.63, the greatest breadth just outside the umbilical shoulder. The costal ratio is 0.76, the greatest breadth at the umbilical bulla. The inner whorls are densely and evenly ribbed with 12 primary ribs per half whorl. There are a total of 18 ribs on the outer whorl, all bullate primaries. They are narrow, very distant, prorsiradiate to the ventrolateral shoulder, where each bears a pronounced bullate ventrolateral tubercle at the smallest diameter visible, but which thereafter declines and effaces, leaving a weakening rib that sweeps forward and is markedly concave over the ventrolateral shoulder. There is a high siphonal keel with long siphonal clavi, corresponding in number to, but displaced adaperturally of, the ventrolateral clavi or their site. The umbilical bullae decline markedly towards the aperture, suggesting that this specimen may be close to maturity.

A magnificent specimen from a limestone concretion from the Carlile Shale near Yankton, South Dakota, in the S. D. Jorgensen collection (Co1970A: fig. 34H, table 3) has one side preserved. This specimen, 83.8 mm in diameter, has a body chamber occupying the last one-half whorl and terminating in a pronounced rostrum 35 mm long. At the smallest diameter visible, approximately 7.5 mm, ribs are single and of equal height. All ribs at larger diameters are primary, narrow, and prorsiradiate. They number 32 per whorl at a diameter of about 11 mm, 26 per whorl at about 19 mm diameter, and 24 per whorl at 83 mm diameter. All arise from low, inconspicuous bullae on the narrowly rounded umbilical shoulder, incline forward on crossing the flank, rise into low bullae on the ventrolateral shoulder, and then bend forward sharply and disappear close to the keel. Bullae are reduced in size near the aperture, and the last two septa are approximated.

The suture, illustrated by Meek (1876a: pl. 7, fig. 2b), is fairly simple and proportioned like that of the juvenile Collignoniceras woollgari figured by Meek (1876a: pl. 7, fig. 1e). Part of a suture near the aperture of the large Jorgensen specimen is shown in fig. 35A.

Discussion:

This is a very rare species. Cobban (1983) initially considered it Collignoniceras praecox (Haas, 1946). The latter, however, has straight, rectiradiate ribs that terminate in sharp horns in contrast to the prorsiradiate ribs of C. vermilionense that bear fowardly inclined ventrolateral bullae.

Occurrence:

Known only from the Carlile Shale in northeastern Nebraska and southeastern and southwestern South Dakota; Collignoniceras praecox Zone.

Derivation of Name:

For Steven D. Jorgensen of Omaha, Nebraska, who donated the holotype and several other specimens from his extensive collections of Cretaceous ammonites.

Types:

Holotype is USNM 498249 (fig. 36A) from the Collignoniceras praecox Zone in the middle Turonian Carlile Shale at USGS Mesozoic locality D13834 in the SW1/4 SW1/4 sec. 25, T. 7 S, R. 6 E, Fall River County, South Dakota. Paratypes USNM 498253 (figs. 35B, 36B–D, K) 498254 (fig. 36H–J), 498251, and 498252 are from the same locality. Paratype USNM 498250 (fig. 34A–C) is from the Carlile Shale at USGS Mesozoic locality D12683 (locality 13 in fig. 1) in the NE1/4 NW1/4 sec. 32, T. 94 N, R. 50 W, Union County, South Dakota.

Diagnosis:

A rather small, evolute species that has prorsiradiate primary and secondary ribs throughout. Primary ribs bear umbilical bullae and inner and outer ventrolateral tubercles. Keel supports a clavate tubercle for each rib. Primary ribs are commonly flared.

Description:

The holotype (fig. 36A) is a small adult, 38.3 mm in diameter, embedded in part of a limestone concretion, so that only one side is visible. Slightly more than one half of the last whorl is body chamber, followed by a long rostrum. The umbilicus is shallow with U/D = 0.42 (table 4). The umbilical shoulder is narrowly rounded. Whorls are apparently higher than wide, are somewhat flattened, and have a narrowly rounded ventrolateral shoulder. The keel is fairly high and accentuated into clavi that correspond to the ribs. Those clavi corresponding to the secondary ribs are low and symmetric; those corresponding to the primary ribs are high and asymmetric with the steep slope forward.

Ornament of the holotype consists of prorsiradiate ribs of unequal heights and umbilical and ventrolateral tubercles as well as siphonal clavi. All ribs are narrow, and all arise on the umbilical shoulder. Primary ribs arise from narrow, umbilical bullae or from narrow, bullate tubercles. Each primary is inclined forward on crossing the flank and then rises into a prominent, arcuate ventrolateral swelling that supports a weak inner ventrolateral tubercle and a weaker outer ventrolateral tubercle before diminishing and disappearing at an acute angle to the keel. Some primaries are flared. There are 12 primaries on the outer whorl. Each pair of primary ribs is separated by one to four low, narrow, secondary ribs that are usually accentuated on the ventrolateral shoulder, but do not bear tubercles. Total primary and secondary rib counts per whorl are as follows: 35 at a diameter of approximately 6 mm, 38 at a diameter of about 14 mm, and 38 at a diameter of about 22.5 mm.

That the holotype is a small adult is revealed by the weakening and disappearance of tubercles on the last part of the body chamber, and by the presence of a long (13.5 mm) rostrum. Only short sections of the suture are visible.

Two paratypes (fig. 36B–D, K and 36H–J) from the same concretion as that of the holotype (fig. 36A) are adults 61 and 65 mm in diameter with umbilical to shell diameter ratios of 0.38 and 0.45, respectively. Both have crushed body chambers with the rostra broken off; the phragmocones are slender and probably somewhat crushed. Ribbing is sparser than that of the holotype, and primaries and secondaries alternate. Another adult paratype (unfigured) from the same concretion has a diameter of 50.5 mm and an umbilical to shell diameter ratio of 0.48. Its body chamber is also crushed, but the prominent rostrum is preserved. Most primary ribs are separated by two secondaries.

The holotype (fig. 36A) and paratypes USNM 498250 (fig. 34A–C) and 498252 represent the robust form of the species. Paratypes USNM 498253 (fig. 36B–D, K) and 498254 (figs. 36H–J) represent the gracile form.

A complete suture is not visible on any specimen. The lateral lobe and adjoining saddles on one of the paratypes is shown in fig. 35B.

Discussion:

Collignoniceras jorgenseni resembles C. vermilionense in size, in its wide umbilicus, and in its conspicuous prorsiradiate ribbing, but C. jorgenseni differs in its dense ribbing and abundant secondaries. Both forms occur with C. praecox and C. percarinatum.

Occurrence:

Known only from the lower part of the Carlile Shale in the Black Hills area of western South Dakota, Collignoniceras praecox Zone.

Types:

Holotype is USNM 318219 (fig. 40D, E) (formerly 103913), paratypes USNM 103913a–e (fig. 40F–I; USNM 103913C not figured), all from the Carlile Shale, middle Turonian Collignoniceras praecox Zone at USGS Mesozoic locality 18872, 3.2 km southeast of Fairburn, Custer County, South Dakota.

Diagnosis:

Moderate to fairly large species with highly variable juvenile whorls that range from densely ribbed with distinct primaries and secondaries to more evenly and sparsly ribbed. Adults have sparser and usually weaker ribs and prominent ventrolateral horns.

Description:

The present collections are nearly all juveniles of the gracile form. Coiling is fairly evolute, with an umbilicus to shell diameter ratio of just under 0.30 (table 5). The whorl section is compressed oval in intercostal section and polygonal in costal section with whorl breadth to height ratios of as little as 0.62. Ribbing is highly variable at small diameters (figs. 39, 40A–C, R–H; 41A–W), but generally shows a marked differentiation into strong and weak primary ribs and weak intercalaries that give these small specimens a highly distinctive appearance. There are up to 10 flared primary ribs per whorl with well-developed umbilical bullae. The primary ribs are narrow, high, and prorsiradiate on the flanks, and each bears a well-developed feebly clavate inner ventrolateral tubercle from which the rib projects sharply forward to a clavate outer ventrolateral tubercle. Between the flared primary ribs are up to four much weaker, nonbullate ribs without ventrolateral tubercles. These specimens closely match one of the paratypes (USNM 103913b, Haas, 1946: pl. 16, fig. 29, cast refigured here as fig. 40H), which shows similar ornament to a whorl height of 14 mm, at which point each weaker rib bears a feeble inner ventrolateral tubercle with pairs of both inner and outer ventrolateral tubercles present on the stronger ribs. Beyond this whorl height, the weaker ribs efface markedly, leaving primary ribs and lirae on the flanks (USNM 498283, fig. 41X, Y). In other specimens (fig. 39G–K) this stage of markedly differentiated ribs is followed, to a diameter of at least 35 mm, by a stage with crowded, dense bullate and nonbullate primary and occasional intercalated ribs that total up to 55 per whorl. These specimens are very similar to paratype USNM 103913d (Haas, 1946: pl. 18, figs. 8, 9; fig. 40F); the ribs are straight and prorsiradiate, and are separated by narrow interspaces. Each rib bears a bullate inner ventrolateral tubercle from which the rib projects abruptly forward and links to a clavate outer ventrolateral tubercle. All these variants have a pronounced siphonal keel with numerous siphonal clavi that are either as numerous or fewer in number per whorl than the ventrolateral tubercles. In middle growth there is an abrupt change to widely spaced ribs (figs. 39X–Z; 40D, E, I; 41X, Y). Bullate primaries alternate with nonbullate long and short ribs, all with conical inner and clavate outer ventrolateral tubercles, the compressed whorl section and feeble flank ornament being distinctive at this size; the holotype is just such a specimen (fig. 40D, E). In ventral view these specimens show the ribs extending in attenuated form forward to intersect the line of the keel at an acute angle, with the interspaces between ribs covered in growth striae, lirae, and riblets. At this stage, the crenulations on the keel are very subdued. In some there are merely irregular elevations; in others (e.g., Haas, 1946: pl. 17, fig. 4; fig. 40I) the keel is almost entire. Our largest specimen of this kind, USNM 498267 (fig. 42), shows progressive effacement of flank ornament and the coalescence of inner and outer ventrolateral tubercles into blunt inner ventrolateral horns. USNM 498284 (fig. 41Z–B′) shows the same transition at only 60 mm diameter.

Juveniles of the robust form are evolute with U/D up to 0.35 (fig. 43E, F; table 5). Their innermost whorls may or may not show differentiation into strong, bullate and weaker, nonbullate ribs. In middle growth, the few available specimens have strong, distant primary ribs with bullae and inner and outer ventrolateral tubercles differentiated to whorl heights of up to 30 mm, with shorter, weaker ribs between. Adults (figs. 44–46) have sparse primary ribs ending in pronounced ventrolateral tubercles or horns.

Several sutures were shown by Haas (1946: figs. 79, 84–90); that of one of the paratypes (USNM 103913e) is reproduced here (fig. 47).

Discussion:

Haas (1946: 156) rightly remarked on the distinctive features of this species: “the accelerated development of this variety from maturity to the latest ontogenetic stage has been alluded to in its name. The differentiation between stronger and weaker ribs and the later disappearance of those of the latter kind cause this variety, of all of the various forms of P. woollgari, most to resemble the genus Prionocyclus. Furthermore it is the only form of, or close to P. woollgari here dealt with that might perhaps be granted the status of an independant species.” Collignoniceras praecox thus differs from C. woollgari regulare in the middle growth stages by the persistence of long and short ribs, with ventrolateral tubercles outnumbering umbilicals. The presence of a near continuous keel where C. woollgari regulare has clavi equal in number to the ventrolateral tubercles is also distinctive. Adult C. woollgari are much larger than those of C. praecox, and have a highly distinctive ribbing and ventral ornament. There are closer similarities between juvenile C. woollgari woollgari and C. praecox, but the strong siphonal clavi of the former, corresponding to the outer ventrolateral tubercles in number, separates them; adults are very different.

Occurrence:

Known with certainty only from the lower part of the middle Turonian Carlile Shale of South Dakota, Collignoniceras praecox Zone.

Types:

Lectotype AMNH 31995 (fig. 48J), designated by Cobban (1983: 18), and paratypes are from “Five miles below the mouth of Vermilion River on the Missouri” (Hall and Meek, 1856: 396). As noted by Cobban (1983: 18), the specimens came from rocks now assigned to the middle Turonian Carlile Shale, probably from the northeast side of Volcano Hill in sec. 3, T. 31 N, R. 5 E, Dixon County, Nebraska.

Diagnosis:

A small species that has closely spaced, prorsiradiate ribs of rather uniform height. Ribs bend forward at the ventrolateral shoulder and fade out at the low keel. Keel notched by low clavi that correspond in number to the ribs.

Description:

Hall and Meek's description is as follows: “Discoidal, depressed; umbilicus wide and shallow; volutions about four or five, all visible in the umbilicus, scarcely one fourth of each embraced in the succeeding one; shell thin; surface marked by thirty-eight to forty-five prominent flexuous sharp ribs some of which originate in the umbilicus, and others upon the lateroventral margin, and all extend to the dorsolateral edge, where they bend abruptly forward, and terminate before reaching the dorsal line, which is marked by a thin sharp carina extending to the aperture. Ribs thickened and sometimes nodose towards the periphery. Our specimens are all casts of the interior with fragments of the shell adhering, and the condition is such as to give no means of determining the character of the septa.”

A suite of small specimens from limestone concretions in the lower part of the Carlile Shale at locality 15 in figure 1, USGS Mesozoic locality D10697, in Fall River County, South Dakota, seem assignable to this species (fig. 48A–H, K–P). The specimens are fairly evolute with umbilical to shell diameter ratios of 0.33–0.48 and 32–38 ribs on the outer whorl. Ribs are prorsiradiate, arise at the umbilicus, cross the flank, and curve forward at the ventrolateral shoulder, where they are accentuated a little or actually form low clavate tubercles. The low keel bears asymmetrical clavi that have the steeper slope on the adoral side. Each siphonal clavus matches a rib.

Discussion:

The presence of a siphonal clavus for each rib supports the assignment to Collignoniceras rather than to Prionocyclus. In later whorls, the species resembles C. vermilionense in having single prorsiradiate ribs that bend forwards sharply on the ventrolateral shoulder. The latter species, however, is much more coarsely ribbed and has larger, more pronounced siphonal clavi.

Occurrence:

Known only from the middle Turonian Carlile Shale, Collignoniceras praecox Zone, of southeastern South Dakota, northeastern Nebraska, and western Minnesota. Specimens figured as Prionocyclus percarinatus by Kirkland (1996: 99, pl. 40, figs. B–F, I) from the Collignoniceras woollgari regulare Subzone in the Mancos Shale of northeastern Arizona have differentiated ribs to a much larger size than on C. percarinatus and represent some other species. Likewise, specimens recorded as Subprionocyclus percarinatus? from the Mancos Shale of west-central New Mexico by Hook et al. (1983: sheet 1) also belong to some other species.

Derivation of Name:

Collignoniceras plus ites (Latin)—descendant of Collignoniceras.

Type Species:

Collignonicerites collisniger n. gen., n. sp.

Diagnosis:

Small, adult at 18 mm or less, involute with compressed whorl section. Distant, blunt umbilical bullae give rise to pairs or groups of ribs, with one or several nonbullate long ribs between; ribs blunt, crowded, prorsiradiate, flexuous, all with small outer ventrolateral clavi. Venter broad, flat, with strong siphonal keel and weak siphonal clavi equal in number to ventrolateral clavi but displaced adaperturally on phragmocone. Ornament declines on adult body chamber, which may be constricted; umbilical bullae present, flank ribs decline but ventrolateral ornament persists; siphonal clavi become irregular.

The suture is very simple with broad bifid E/L with few incisions, narrower L, and nearly entire L/U₂.

Discussion:

Decline in ornament and the development of constrictions indicates that the species attains maturity at 17 mm or less, while the very simple adult suture indicates that these specimens are more than mere juveniles of some larger form. Collignonicerites resembles Collignoniceras; the very simple suture of Collignoniceras (e.g., Matsumoto, 1965: text-fig. 6A) is retained to maturity in Collignonicerites. The phragmocone ornament of Collignonicerites with outer ventrolateral clavi equal in number to siphonal clavi and ribs springing in groups from bullae resembles that of the ornamented earliest developmental stages of Collignoniceras with which Collignonicerites collisniger gen. et sp. nov. co-occurs.

Collignonicerites is an analog of Prionocyclites Kennedy, 1988, a diminitive genus closely related to Prionocyclus. Species of the two genera share certain features common to progenetic dwarfs, including a greatly simplified suture. However, they differ in that species of Prionocyclites are more evolute and lack massive bullae giving rise to groups of ribs, having instead narrow, distant, single bullate primaries separated by nonbullate primaries and secondaries, an undulose rather than serrated keel, and a body chamber with distant feeble bullae, narrow, single flank ribs, and an apertural constriction flanked by collar-ribs.

Progenetic species have increasingly been described in recent publications on Late Cretaceous ammonites, as noted by Wright (1996: xviii; see, for instance, Wright and Kennedy, 1980; Kennedy, 1988; Kennedy and Cobban, 1990a, 1990b). Dimorphism has been recognized in these dwarfs, demonstrating that they are not the microconchs of co-occurring larger taxa. Because of their small size, these dwarf taxa have, in general, only been detected in exceptionally preserved faunas, such as those found in the concretions in shale and mudstone facies of the U.S. Western Interior.

Occurrence:

Middle Turonian Collignoniceras woollgari regulare Subzone of the Black Hills only.

Derivation of Name:

collis + niger (Latin) black hills, from the type area.

Types:

Holotype is USNM 498294 (fig. 49M, R–T), paratypes USNM 498295–498302 (fig. 49A–K, N–Q; 498301 not illustrated), from the middle Turonian Carlile Shale, Collignoniceras woollgari regulare Subzone at locality 12 in fig. 1: USGS Mesozoic locality D13832, Carlile Shale, middle Turonian, C. woollgari regulare Subzone, sec. 35, T. 8 S, R. 1 E, Fall River County, South Dakota.

Diagnosis:

With the characters of the genus.

Description:

Coiling fairly involute (U/D = 0.26) and umbilicus moderately deep (table 6). The umbilical wall is flattened, subvertical, with an evenly rounded shoulder. The whorl section is compressed, with greatest breadth below midflank in intercostal section, and shows broadly rounded inner flanks, flattened convergent outer flanks, and a relatively broad, flattened venter with a sharp siphonal keel. The greatest breadth is at the umbilical bullae in costal section. In strongly ornamented variants, blunt umbilical bullae, four to six per whorl, are present in middle growth. The bullae give rise to two or three primary ribs with up to three nonbullate long ribs separating the bullate groups. These nonbullate ribs arise either singly or in pairs at the umbilical shoulder to give a total of 16 ribs per half whorl. Ribs are broad, crowded, flexuous, and prorsiradiate, and each bears a small outer ventrolateral clavus from which the rib projects forward and declines in strength, intersecting the line of the siphonal keel in an acute chevron. The keel has even siphonal clavi, equal in number to but displaced adaperturally of the ventrolateral clavi. In feebly ornamented variants, the umbilical bullae are weak; the flanks bear only striae and lirae on the inner part but the ventrolateral part is similar to that already described. The umbilical bullae may decline on the adult body chamber, which may be constricted, while the crenulations on the siphonal keel become irregular.

The suture is the same as for the genus.

Discussion:

See under genus.

Occurrence:

As for types.

Type Species:

Prionocyclus serratocarinatus Meek, 1871: 298, non Stoliczka, 1865: pl. 32, fig. 31, = Prionocyclus wyomingensis Meek, 1876a: 452.

Diagnosis:

Medium to large, adult up to 300 mm in diameter. Size-related dimorphism not recognized (due to paucity of adults), but the middle growth stages of all species occur as involute, relatively compressed, feebly ornamented gracile forms or more evolute, less compressed, strongly ornamented, robust forms. Ornament highly variable, typically of stronger primary ribs with umbilical, inner, and outer ventrolateral tubercles at some stage in ontogeny separated by weaker nonbullate and intercalated ribs that have inner and outer ventrolateral tubercles at some stage in ontogeny. Outer ventrolateral tubercles may decline or not, inner ventrolateral tubercles may bear long septate spines; faint inner lateral tubercles may develop during later growth stages. Siphonal keel is strong to weak, and finely serrated, with the number of serrations exceeding the number of ribs.

Discussion:

The type species of Prionocyclus and Collignoniceras are distinct, especially in the adult stage, and juveniles can be separated because the keel of Collignoniceras has siphonal clavi equal in number to that of the ventrolateral tubercles, whereas in Prionocyclus the serrations greatly outnumber the ribs (compare figs. 17, 18 and figs. 78, 84). In Prionocyclus, the marked differentiation of ribbing present in the early ontogenetic stages of certain variants of C. praecox (e.g., fig. 41F–U) persists to maturity.

Germariceras Breistroffer, 1947 (unpaged), with Ammonites germari Reuss, 1845 (fig. 109K), from the upper Turonian of Czech Republic as type species, is best known from the lithographs of Fritsch (1872: pl. 14, figs. 1, 2; pl. 16, fig. 7), and was recently revised by Kaplan (1988). It is here shown to be common and widespread in the U.S. Western Interior, and shows no characters that merit separation from Prionocyclus.

Occurrence:

Middle Turonian of the U.S. Western Interior, Gulf Coast, and northern Mexico; upper Turonian of the U.S. Western Interior, Gulf Coast, and northern Mexico, Tunisia, Japan, Czech Republic, Germany, and Kazakhstan. Records from Southeast France (Middlemiss and Moullade, 1968) are unsubstantiated.

Types:

Lectotype, by subsequent designation of Matsumoto 1965: 19, is USNM 22941, the original of Stanton's 1894: plate 42, figures 5, 6 (fig. 50C–E); figured paralectotype is USNM 22941a, the original of Stanton's plate 42, figures 7, 8 (fig. 50A, B). They are from the Codell Sandstone (Pugnellus Sandstone) of Williams Creek and Poison Canyon, Huerfano Park, Colorado. Stanton refers to many specimens from Huerfano Park and a few from Coalville, Utah: all are paralectotypes (e.g., fig. 50F–H).

Diagnosis:

A moderately evolute fairly large species ornamented by straight, prorsiradiate primary and secondary ribs terminating in ventrolateral tubercles. Low keel differentiated into low asymmetric clavi slightly more numerous than the ribs. Inner whorls usually densely ribbed. Primary ribs on outer whorl support umbilical bullae or nodate umbilical tubercles. Inner ventrolateral tubercles on adult body chamber may enlarge into conspicuous spines.

Description:

The lectotype is a small, robust specimen (Stanton, 1894: pl. 42, figs. 5, 6; Matsumoto, 1965: 19, pl. 17, fig. 3a–c; fig. 50C–E). Measurements in millimeters and ratios from a plaster cast are as follows: D = 31.0, Wb = 14.2 (46%), Wh = 12.0 (39%), Wb:Wh = 1.18, U = 10.6 (34%). Primary and secondary ribs arise on the umbilical wall and are straight and prorsiradiate on crossing the flanks. They number 29 per whorl at a diameter of approximately 7.5 mm, and 29 per whorl at a diameter of about 19 mm. Primary ribs support umbilical bullae, prominent clavate inner ventrolateral tubercles, and weak outer ventrolateral clavi. Some secondaries bear weaker ventrolateral tubercles. All ribs bend forward on the ventrolateral shoulder and fade out at an angle toward the keel. Most primaries and secondaries alternate. Toward the adapertural end, the inner ventrolateral tubercles on the primary ribs enlarge and become hornlike, projecting outward at a low angle to the venter. In this manner, the specimen is much like the last part of the phragmocone of the remarkable spined individual figured by Kennedy and Cobban (1976, pl. 8, fig. 1; fig. 58) from the Carlile Shale of Kansas. On the older part of the outer whorl of Stanton's specimen, the keel is differentiated into low clavi that correspond to the ribs, but on the younger part, the clavi seem to number about two per rib.

The other specimen figured by Stanton (1894: pl. 42, fig. 7; fig. 50A, B) is a small, gracile, evolute specimen 21.0 mm in diameter with an umbilical ratio of 49% (measurements from a plaster cast). The keel is low and appears to be differentiated into asymmetric clavi that are less numerous than the ribs. Ribs are narrow and prorsiradiate; they number 35 on the outer whorl, where one or two secondaries separate primaries.

In the lower, Hoplitoides sandovalensis Subzone of the Prionocyclus hyatti Zone, a collection from a narrow horizon in the Semilla Sandstone Member of the Mancos Shale at USGS locality 28873 (locality 41 in fig. 1) is typical. It and other collections reveal that both robust and gracile forms are present in similar numbers.

In the robust form (figs. 55C, D, 56–58), nuclei show great variation. Coiling is very evolute, with the umbilical seam indented to accommodate the inner ventrolateral tubercles of the inner whorl, the umbilicus is of moderate depth, the umbilical wall flattened and subvertical, the umbilical shoulder quite narrowly rounded, the whorls slightly compressed to depressed, quadrate in intercostal section, and octagonal in costal section (table 7). At one extreme there are as few as 20 ribs per whorl, with up to 30 at the other. The ribs are all bullate primaries of equal development, strong, straight, and prorsiradiate, and strengthen across the flanks to strong conical to clavate inner ventrolateral tubercles. A broad prorsiradiate rib connects an inner ventrolateral tubercle to a strong outer ventrolateral clavus, and a smooth zone separates the ribs from a strong siphonal keel, with clavi occupying the interspaces between tubercles (fig. 56C–D). As size increases, the ribs become very coarse and massive, with strong (fig. 56H–J) to weak bullae (fig. 56C, D), with as few as 16 ribs per whorl. Sometimes the bullae are of variable strength (fig. 56E–G), and displaced out from the umbilical shoulder. The outer ventrolateral clavi are assimilated into the inner ventrolateral tubercles, which enlarge into massive blunt horns that project outward but usually not significantly above the level of the venter (fig. 56E–J). Other robust individuals have nuclei in which strong, bullate primary ribs are separated by up to three weaker nonbullate primaries, with a total of up to 45 ribs per whorl. This differentiation persists into middle growth. The bullate primaries have strong umbilical bullae and inner and outer ventrolateral tubercles. The nonbullate primaries sometimes connect to the umbilical bullae as mere striae and have weak ventrolateral tubercles, in some cases, only outer ones. In some specimens (fig. 58) the stronger primaries develop massive horns or spines, with hornless ribs between. The largest robust individual at hand is 270 mm in diameter.

Nuclei of the gracile form (figs. 51A–R, V–Y, 52A–L, 53, 54, 55E–J) overlap to a degree with those of the robust form. They are more compressed, with a broad, shallow umbilicus (table 7), and have up to 50 ribs per whorl that may be even (fig. 51M–O) or vary greatly in strength (fig. 51A–I). The stronger ribs are flared, usually bullate, with inner and outer ventrolateral tubercles; the weaker ribs lack bullae and have feeble or no inner ventrolateral tubercles. This style of ornament may persist into middle growth, and there are gracile forms with dense, even ribs that may reduce to mere striae (fig. 51N) and others with ribbing of variable strength and tubercle development (fig. 52K, L). Inner and outer ventrolateral tubercles remain separate and do not merge into horns, as in the robust form; nonbullate ribs may lack an inner ventrolateral tubercle and have much weaker outer ventrolateral tubercles than on the bullate primaries. The keel is broadly and irregularly undulose.

Both robust and gracile forms show enormous variation in ribbing and tuberculation style as well as timing of ontogenetic changes in ornament. This is more readily appreciated from the illustrations (figs. 50–60) than from mere description.

Prionocyclus hyatti from the upper part of its zonal range is illustrated by collections from the Carlile Shale of Kansas, where the species occurs as fragments, often of large body chambers, in ironstone concretions. Original aragonite shell is often preserved (fig. 57). Many of the specimens we have seen from Kansas are large, up to 300 mm in diameter. Juveniles are as variable as those from the Hoplitoides sandovalensis Subzone in New Mexico and elsewhere already described, with even, coarse to fine ribbing as well as markedly differentiated weak and strong ribs. This variation is maintained into middle growth, and most individuals have strong, bullate primary ribs with massive ventrolateral horns and weaker, nonbullate intercalated ribs between that have weak ventrolateral tubercles. At the largest diameters, fragments may bear as few as six ribs with massive ventrolateral horns per half whorl, and some specimens show the horns to have been septate, with a long spine (fig. 59).

These large specimens commonly show an outward migration of the umbilical bullae, which become conical and occupy an inner flank position. The keel of these specimens is variable, from broadly undulose with coarse clavi only slightly more numerous than ventrolateral tubercles (fig. 57A, B) to others where the crenulations are minute and far more numerous.

The suture (fig. 60) has moderately incised elements; E/L is broad and bifid, and L is narrower and bifid, as is L/U₂.

Discussion:

Prionocyclus hyatti is the species of the genus closest to Collignoniceras, discussed above. Juvenile stages show certain common characters, but middle and late growth stages are distinct. Prionocyclus hyatti differs from the most closely comparable Prionocyclus, P. macombi, as follows: the robust forms of the two species may have a degree of overlap in their coiling, whorl section, and expansion rate, but small and medium-sized individuals of P. macombi never develop ventrolateral horns as massive as those of P. hyatti, nor the striking differentiation into strong horned ribs with umbilical bullae, and weak, nonbullate hornless ribs. The gracile forms of P. macombi are much more compressed, higher-whorled, and more involute than the corresponding forms of P. hyatti. The ribbing is also denser and finer in P. macombi with the ribs often reduced to mere striae, and the inner and outer ventrolateral tubercles of the inner whorls replaced by a single ventrolateral clavus at an early stage.

Occurrence:

Widely distributed in the Western Interior from northern Montana southward into Trans-Pecos Texas and eastward from there into central and northern Texas (fig. 61). Also known from northern Chihuahua, Mexico, and Kazakhstan (Marcinowski et al., 1996).

Type:

Lectotype, here designated, is the original of Fritsch, 1872: plate 6, figure 4, no. 03144 in the Collections of the Narodni Museum, Prague, from the Turonian of Wehlovice, in the Czech Republic (fig. 108C is a plaster cast taken from an external mold of the type).

Diagnosis:

A moderate-sized, fairly evolute species that has whorls higher than wide with flattened flanks. Ornament of numerous prorsiradiate ribs with primaries usually separated by two or three secondaries.

Description:

The lectotype is 41 mm in diameter. Coiling is evolute, with U/D = 0.42. The umbilicus is shallow, with a feebly convex wall, and more narrowly rounded umbilical shoulder. On the last half whorl, six or seven primary ribs arise on the umbilical wall, and strengthen into feeble bullae perched on the umbilical shoulder. The ribs are coarse, straight, and prorsiradiate on the flanks, with inner and outer ventrolateral clavi; the venter is not preserved. These strong primaries are separated by single much weaker ribs that lack umbilical bullae and inner ventrolateral tubercles. The poorly preserved inner whorls are much more finely ribbed.

Western Interior specimens referred to the species have finely and evenly ribbed inner whorls (fig. 62A, D, F, L, O); the ribs are equal, crowded, straight, and prorsiradiate on the flanks. This stage is succeeded, at variable diameters, by a growth stage in which the ribs differentiate into stronger primaries with umbilical bullae, strong inner, and weaker outer ventrolateral tubercles, separated by much weaker ribs that lack bullae and inner ventrolateral tubercles, but have feeble or effaced outer ventrolaterals; as many as four and as few as one of these weaker ribs may separate the stronger primaries. Ribbing of this type extends onto the body chamber of USNM 498339 (fig. 62P), interpreted as an adult.

The suture is moderately incised, as in P. hyatti.

Discussion:

Prionocyclus albinus may represent a paedomorphic derivative of Prionocyclus hyatti in which the crowded ornament and variable rib strength of juveniles of the latter are retained to maturity. Small specimens of the two species are liable to be confused, but in middle growth, the change to more distant ribbing in P. hyatti is distinctive, and the two species reach maturity at widely differing diameters.

Occurrence:

Prionocyclus hyatti Zone, Smith County, Kansas; Emery County, Utah; Sandoval County, New Mexico; Dallas County, Texas. The type material is from the Turonian of the Czech Republic.

Types:

The lectotype here designated is USNM 20259, the original of Meek, 1876b: plate 2, figure 3 (fig. 63A, B), from the Juana Lopez Member of the Carlile Shale of Colfax County, New Mexico, middle Turonian Prionocyclus macombi Zone. Meek refers to more than one specimen of Prionocyclus? macombi in his original account, indicating the species to be based on a type series. The lectotype is the original of his plate 2, figure 3a–c, and the original of his figure 3d may conceivably be the inner whorls of this specimen.

Diagnosis:

A moderate-size species that occurs as an early form with arched venter and a later form with flattened venter. Keel low and notched into as many as three or four clavi per rib. The gracile form is exceptionally compressed and has densely ribbed innermost whorls; the outer adult whorls are nearly smooth. The robust form has coarser and stronger ornament than the gracile form; ribs support nodate to bullate umbilical tubercles and nodate to spinose inner ventrolateral tubercles, whereas outer ventrolateral clavi are barely perceptible or absent.

Description:

Robust and gracile forms of Prionocyclus macombi are distinct from the early growth stages on. During middle and later growth stages, it is also possible to recognize an early form of the species, where the venter is distinctively arched and rounded (figs. 68L, 71A–D, 72, 73) and a late form in which the venter is flattened (e.g., fig. 68P).

The earliest growth stages are highly variable and individuals may be nearly smooth (fig. 67Y, Z) to densely ribbed (fig. 67A–E) in the gracile form. The smoothest variants have distant umbilical bullae and tiny outer ventrolateral clavi, even though flank ornament is virtually absent. Densely ribbed juveniles generally have up to 16 strong primary ribs, sometimes feebly bullate, and giving rise to bundles of ribs. One to four weaker primary and intercalated ribs occur between the stronger ribs and extend to the umbilicus or arise on the inner flank. Ribs are prorsiradiate and straight to feebly flexuous across the flanks. They project forward and are concave over the ventrolateral shoulder. Weak inner ventrolateral and clavate outer ventrolateral tubercles are present on the stronger primary ribs; the weaker primary and intercalated ribs are feebly or nontuberculate. This densely ribbed stage terminates abruptly in most specimens by about 15–20 mm diameter or less.

Dimensions, ratios, and number of ribs per whorl of three nuclei are given in table 8. At this stage, the shell is compressed and high-whorled with a small umbilicus comprising as little as 17% of the shell diameter with whorl breadth to height ratios of as little as 0.5. The umbilical wall inclines outward and merges with a broadly rounded umbilical shoulder. The flanks are flattened and subparallel, and the ventrolateral shoulders are broadly rounded. The venter is arched in early forms, and more flattened in later ones. Delicate umbilical bullae of variable strength and generally 14–20 per whorl perch on the umbilical shoulder (fig. 67Q–X). They give rise to narrow, flexuous prorsiradiate ribs that terminate in small clavate to bullate inner ventrolateral tubercles. Outer ventrolateral tubercles may also be present, linked to the inner by prorsiradiate ribs, but disappear in early middle growth. The wide interspaces between these bullate primaries bear weak ribs that arise at the umbilical seam or low on the flanks plus lirae and growth striae (fig. 67Q–X). These weaker ribs may bear inner, but not outer ventrolateral tubercles, giving the shell a distinctive appearance when viewed ventrally (fig. 69B, C). Ornament sweeps forward and is concave over the ventrolateral shoulder, forming an acute ventral chevron. The keel is minutely and evenly serrated, the serrations far exceeding the ribs in number (figs. 69A–C, F, G; 70A–C). The largest gracile forms are still septate at 150 mm diameter (table 9). These specimens are ornamented by distant, narrow prorsiradiate ribs with weak umbilical bullae, up to 26 per whorl, separated by broad interspaces that are smooth on molds. Most specimens only have inner ventrolateral clavi at this stage, while there are some specimens with clavi intercalated between the ribs or even short intercalated ribs. Riblets and striae form an acute chevron on the venter, while the keel remains minutely serrated when well preserved.

Robust forms have a much wider umbilicus and the whorl section varies from slightly compressed to depressed. In juveniles (fig. 67F–P) there are usually approximately 12 prominent umbilical bullae per whorl. These give rise to distant, narrow, rounded, straight, prorsiradiate primary ribs separated by wide interspaces, smooth on most molds. Bullae may be equal in strength or vary, while a few specimens have shorter intercalated ribs (fig. 69H, I). All ribs terminate in conical to feebly clavate inner ventrolateral tubercles, which may be equal or of variable strength. Broad ribs sweep forward to feeble outer ventrolateral clavi, which are lost early in middle growth. The ventral keel is entire and minutely serrated. If inner ventrolateral tubercles are strong, the umbilical seam and wall of the succeeding whorl may be notched to accommodate them (fig. 69H). The venter is rounded or arched in early forms (fig. 68J–L), flattened in later ones (fig. 68F–I, O, P). As size increases, ornament may coarsen markedly, and a common variant has a depressed, polygonal coastal whorl section, strong conical umbilical bullae displaced out a little from the umbilical wall, low, broad, distant radial ribs, effaced at midflank, and blunt, conical inner ventrolateral horns. There may be low, blunt ventrolateral ribs with feeble tubercles between (figs. 72H, I). The keel commonly lacks regular serrations on the internal mold.

The largest fragments of the robust form are still septate at whorl heights of 70 mm, corresponding to an estimated diameter of 220 mm (table 9). Ornament consists of coarse, distant bituberculate ribs, the inner ventrolateral tubercles developing into sharp horns on molds, while there are occasional feeble intercalated ventrolateral tubercles. A body chamber fragment with a whorl height of 90 mm shows weakening umbilical bullae and a sharpening of ribs plus strong growth striae and lirae on the umbilical wall suggesting maturity at a size of 220–250 mm diameter. The fairly simple suture (fig. 74) has been illustrated by Meek (1876b: pl. 2, fig. 3c) and by Stanton (1894: pl. 41, fig. 3).

Discussion:

Differences between Prionocyclus macombi and P. hyatti are discussed above. Prionocyclus bosquensis Kennedy, 1988 (86, pl. 18, figs. 1–3, 10, 11; text-fig. 29a, d, f–i; figs. 76, 77), which is known only from crushed specimens, differs from P. macombi in showing bunching of ribs at umbilical bullae as well as persistence of inner and outer ventrolateral tubercles in middle growth. P. wyomingensis (figs. 78–87) is known mostly from the gracile form, which exhibits much stronger, coarser ribbing than that of P. macombi with slender whorls. In addition, in P. wyomingensis the ribs sometimes arise in groups from bullae, and an inner lateral bulge or tubercle and a fingerlike septate horn on the inner ventrolateral tubercle develop at maturity.

Occurrence:

Prionocyclus macombi has been found in a wide belt paralleling the western shoreline of the basal late Turonian seaway that extends from western South Dakota southwestward to central Utah and then southeastward through most of New Mexico (fig. 75). The species is also known from north-central Texas.

Types:

Holotype is OUM KT 3854 (fig. 76D); there are numerous paratypes of which the following are illustrated: OUM KT 3281 (fig. 76B), 3801b (fig. 76C), 3858 (fig. 76A), 3868 (fig. 77B), 3869 (fig. 76E), 3870 (fig. 77A), and 3873 (fig. 77C), from the top 6–7 m of the South Bosque Formation, Cement Works, 10 km (6 mi) southwest of Waco, McLennan County; also OUM KT 5375–85, pyritic juveniles from the same locality and horizon; OUM KT 5372a, b collected in situ 3 m below the base of the Austin Chalk at this locality; OUM KT 5373a, b from 1 m below the Austin Chalk; upper Turonian Scaphites whitfieldi zone.

Diagnosis:

A small densely ribbed species with a minutely notched keel. Ribs flexuous and not distinctly separated into primaries and secondaries.

Description:

This species has been fully described by Kennedy (1988: 86, 87): “Most specimens are 10–45 mm diameter, are crushed, and retain original aragonitic shell. Coiling is fairly involute, with U = 29%. Ornament is highly variable. At one extreme are very finely ornamented individuals. These have very dense, crowded, narrow, flexuous prorsiradiate ribs, every fifth to sixth strengthened, with a tiny umbilicolateral bulla, a bullate inner ventrolateral, and an obliquely placed outer ventrolateral tubercle. The intermediate ribs generally lack umbilical bullae, and have very faint or no inner and outer ventrolaterals. There is a strong, minutely serrated siphonal keel. A few specimens may even lack differentiated ribs and bear fine, even ornament, without tubercles; some individuals show groups of 3 or so ribs arising from a bulla while all specimens bear long intercalated ribs inserted on the inner flank. These specimens usually retain their outer ventrolateral tubercles. They are linked, by strengthening of tubercles and progressive decline of the weaker, feebly tuberculate ribs to much rarer individuals with distant ribs with umbilical bullae, strong inner and weak outer ventrolaterals, the interspaces with weak to obsolete flank ribs, but short intercalated ribs on the ventrolateral shoulders and venter. There are a few much larger fragments, with whorl heights of up to 53 mm. All of these show strong distant ribs with umbilical bullae, prominent inner ventrolateral spines or tubercles, weak, or no outer ventrolaterals, and groups of riblets and growth striae extending from the inner ventrolateral nodes towards the mid-venter. Between these ribs are much finer intercalated riblets and lirae. There is a strong crenulate siphonal keel. Sutures not seen.”

Discussion:

See Kennedy (1988: 88).

Occurrence:

As for types.

Types:

Lectotype, by the subsequent designation of Matsumoto, 1965: 18 is USNM 7729, the original of Stanton, 1894: plate 40, figure 3 (fig. 78); two paralectotypes have the same number and are the originals of Stanton, 1894: plate 40, figures 1, 2 (figs. 79, 80). A further probable unfigured paralectotype bears the number 7729D, and is shown in figures 82, 83. All are from what is now known as the Wall Creek Sandstone Member of the Frontier Formation in the Medicine Bow River valley of Southeast Wyoming (fide Cobban, 1984a: 86).

Diagnosis:

A large species for the genus; moderately evolute; keel notched into more siphonal clavi than ribs. Gracile form has closely spaced prorsiradiate primary and secondary ribs. Primary ribs bear lengthy umbilical bullae that may divide into shorter umbilical bullae and bullate or nodate inner lateral tubercles. All primaries bear nodate inner ventrolateral tubercles and weaker clavate to bullate outer ventrolateral tubercles. Robust form has coarse ribs that support prominent nodate umbilical tubercles, nodate inner ventrolateral tubercles, and weak outer ventrolateral clavi.

Description:

The robust form is rare (figs. 84A–F, 85D, E, H, I). Coiling is evolute with U/D = 0.30–0.37 in the available material (table 10); the umbilicus broad, the umbilical wall flattened and inclined outward, with grooves to accommodate the inner ventrolateral spines of the preceding whorl (fig. 85E). The umbilical shoulder is narrowly rounded, the whorl section slightly compressed to slightly depressed, with the greatest breadth at the umbilical bullae costally and just outside the umbilical shoulder intercostally.

Ornament is highly variable. At one extreme are very coarsely ribbed individuals with only 16 or 17 ribs per whorl. Ribs arise at the umbilical seam and strengthen into massive conical umbilical bullae, broaden and are straight and prorsiradiate across the flanks, and develop massive septate inner ventrolateral spines that generally appear as large clavi on the mold when the spines have broken off. The rib profile is somewhat concave between bulla and spine (fig. 85H, I). Broad ribs sweep forward across the ventrolateral shoulder to outer ventrolateral clavi and a smooth zone separates them from the strong and minutely serrated siphonal keel.

At the other extreme (fig. 85D, E) are similarly proportioned individuals that have 17 sharp to spinose umbilical tubercles in middle growth, each of which gives rise to a strong concave to straight and rectiradiate adapical primary rib and a much weaker adapertural primary rib, which loop to a strong inner ventrolateral clavus/spine, the arrangement resembling a bow. Broad ribs sweep forward over the ventrolateral shoulder and connect to weaker outer ventrolateral clavi. Between the looped, bullate ribs are one or two nonbullate ribs that extend to the umbilical seam or arise on the inner flanks and develop much weaker ventrolateral tubercles, the arrangement giving the shell a highly irregular ornament. The largest robust individual seen is 83 mm in diameter.

Gracile individuals are common (figs. 78–81; ?82, ?83; 84G–J, 85A–C, F, G). At 40 mm diameter, coiling is evolute, with U/D = 0.26 (table 10); the umbilicus is shallow, with a low flattened umbilical wall. The whorls are high and compressed (whorl breadth to height ratio averages 0.79), with fine, dense, crowded ribs. There are up to 12 weak umbilical bullae that give rise to single or paired ribs, with single nonbullate ribs between that extend to the umbilicus or not, yielding a total of 44–48 ribs per whorl. Ribs are crowded, flexuous, and prorsiradiate, with small bullate to clavate inner, and clavate outer ventrolateral tubercles.

In middle growth, specimens have up to 70 ribs per whorl. There are up to 18 bullae per whorl, initially at the umbilical shoulder, but tending to move out to the inner flanks, when a new bulla develops (fig. 81C). They are the bases of septate umbilical spines, and give rise to pairs of coarse ribs that are straight and prorsiradiate and initially loop to outer ventrolateral tubercles that are also the bases of septate spines. As size increases, the tendency to loop declines and the adapertural rib of the pair may detatch. There are one to six weaker, nonbullate long ribs between the bullate ones, each of which may develop a weak inner ventrolateral tubercle.

The ribs sweep forward over the ventrolateral shoulder to small, obliquely placed outer ventrolateral tubercles and form an acute chevron with the high and minutely serrated siphonal keel. The largest gracile individuals are 220–230 mm diameter. At maturity, the bullate ribs strengthen markedly and are very coarse, high, and barlike. Where well-preserved, they bear long inner lateral and inner ventrolateral spines, while sharp outer ventrolateral clavi are also present. Between are up to three much weaker, narrow, sharp long ribs that lack any trace of a tubercle. This coarseness and marked differentiation of the main ribs gives a highly characteristic appearance to the shell.

The largest collection studied consists of 73 specimens from the Frontier Formation at USGS Mesozoic locality D9244 in southeastern Wyoming. Of these specimens 61 are the gracile form and 12 are the robust form.

The suture is fairly simple and typical of the genus. The suture from White (1880) is shown here (fig. 87).

Discussion:

Differences between P. wyomingensis, P. macombi, and P. bosquensis are noted above. P. wyomingensis most closely resembles P. novimexicanus (Marcou, 1858) (figs. 88–101), which is presumably its descendant, but the latter is even more compressed, has flexuous ribs, seldom develops the umbilical and inner lateral tuberculation of P. wyomingensis and loses the outer ventrolateral tubercles at a very early stage so that the primary ribs are effectively bituberculate.

A remarkable pathological specimen (collected by J. I. Kirkland, Salt Lake City, Utah), USNM 475903 (fig. 86), from the Juana Lopez member of the Mancos Shale in the SE¼ sec. 4, T. 12 S, R. 1 E, Garfield County, Colorado, lacks a siphonal keel (fig. 86).

Occurrence:

Prionocyclus wyomingensis is widely distributed in the Western Interior of the United States from northwestern Montana south through much of New Mexico, and from east-central Utah to southwestern Kansas. It has also been figured recently from Alberta, Canada (Hall et al., 1994) and is known from Japan (Matsumoto, 1971).

Types:

The lectotype, here designated, of Ammonites novimexicani Marcou, 1858, is BMNH C49764 (fig. 88A–C), either from near Albuquerque, New Mexico, or La Lunes, New Mexico. Marcou specifically mentions two specimens in his account, and lectotype designation is necessary. The holotype of Prionocyclus wyomingensis elegans Haas, 1946 (a synonym), is the original of Whitefield, 1880: plate 14, figure 2, from Beaver Creek, near Camp Jenney, South Dakota, USNM 12283 (fig. 89A, B).

Diagnosis:

This large, moderately evolute species has a keel notched into small siphonal tubercles more numerous than the ribs. The gracile form has dense, flexuous primary and secondary ribs. Primary ribs arise from elongated umbilical bullae, each of which is rarely divided into a shorter umbilical bulla and a small, nodate inner lateral tubercle. All primaries bear rounded to clavate inner ventrolateral tubercles. Outer ventrolateral tubercles are usually absent, and very weak if present. The robust form is more evolute and more sparsely ribbed. Looped ribs may connect umbilical and inner ventrolateral tubercles in both gracile and robust forms.

Description:

The best example of the robust form is USNM 498417 (fig. 99F, G). Coiling is very evolute, with U/D = 0.48, the umbilical wall flattened and inclined outward, the umbilical shoulder broadly rounded, the flanks convergent with the greatest breadth at the umbilical shoulder intercostally and at the umbilical bulla in costal section. The whorl section is compressed, with a costal whorl breadth to height ratio of 0.73 up to a shell diameter of 60 mm (table 11). Ornament consists of blunt umbilical bullae, 18 per whorl. These give rise to broad, low, straight prorsiradiate ribs that weaken markedly at midflank, and connect to blunt inner ventrolateral bullae. Broad ribs sweep forward and decline, forming an acute chevron with the minutely serrated siphonal keel; there is no trace of an outer ventrolateral tubercle. Beyond 60 mm, the bullae weaken progressively, and commonly give rise to pairs of ribs, which may loop to the inner ventrolateral bullae (fig. 100C, D) or not. Between are one or two weaker nonbullate ribs, arising at the umbilical shoulder or low on the flanks with feeble inner ventrolateral tubercles or not. The ribs become feebly flexuous at this stage.

The gracile form is represented by numerous specimens (figs. 88–95, 98A–C). Coiling is moderately evolute, with a shallow umbilicus with U/D = 0.26–0.30 between 50 and 100 mm shell diameter; the umbilicus is shallow, with a flattened wall. The whorl section is compressed, with whorl breadth to height ratios of 0.5–0.7 (table 11), the greatest breadth at the umbilical bullae in costal section and just outside the umbilical shoulder intercostally.

The earliest growth stages seen are characterized by very fine, dense, crowded ornament. Feeble umbilical bullae give rise to pairs or groups of three ribs; between are up to nine ribs which arise at the umbilical shoulder, low, or high on the flanks. The degree of differentiation between strong and bullate and weak and nonbullate ribs varies greatly between individuals (figs. 90–92), with up to 90 ribs per whorl. In middle growth, to a diameter of 70–80 mm, ribbing varies greatly in strength and density between individuals (compare fig. 90L and fig. 99A, B). Typically, there are 14–18 bullae per whorl that give rise to pairs or groups of ribs, with nonbullate intercalaries between, the bullate ribs looping in pairs to inner ventrolateral clavi, the nonbullate ribs with feeble inner ventrolateral tubercles or not. Feeble outer ventrolateral tubercles are present only at diameters of less than 15–20 mm. Beyond, ribs sweep forward over the ventrolateral shoulder to form an acute chevron. The siphonal keel is high, strong, and minutely serrated.

An adult of the gracile form has a maximum diameter of 386 mm (figs. 94, 95). It retains the crowded ornament of ribs of varying strengths to a diameter of 170 mm, beyond which the minor ribs decline progressively so that by the middle section of the body chamber, ornament consists of very distant, coarse, convex prorsiradiate ribs with strong, subspinose umbilical bullae and enormous, slender septate inner ventrolateral horns that persist to the last section of the body chamber. Just before the adult aperture, ribbing stops and the last section is covered in dense irregular riblets, lirae, and striae.

USNM 498423 (figs. 96, 97) is an uncrushed body chamber mold. The whorl height is 98 mm at the end of the phragmocone, and the diameter of the specimen is 380 mm, which suggests a total diameter of over 400 mm. The whorl section at the end of the phragmocone is trapezoidal with a whorl breadth to height ratio of 0.95. Ornament consists of strong, distant, coarse primary ribs, with umbilical bullae that decline in strength as size increases. There are massive conical inner ventrolateral tubercles at the end of the phragmocone and beginning of the body chamber. They weaken on the later part of the body chamber. Narrow ribs project forward over the venter to form a chevron, with finer and irregular riblets between. The siphonal keel is blunt on the mold, and irregularly notched.

The suture has a broad, bifid E/L, narrow L, and bifid L/U₂ (fig. 101).

Discussion:

Prionocyclus novimexicanus most closely resembles its presumed ancestor, P. wyomingensis (figs. 78–87); differences are discussed above. Prionocyclus quadratus (figs. 102–107) and P. germari (figs. 109–119) never show the marked differentiation of rib strength of juvenile P. novimexicanus; instead the ribbing is even. The whorls are never as depressed or as finely ribbed, although P. quadratus and P. germari lose their outer ventrolateral clavi at very small diameters, as does P. novimexicanus. Prionocyclus quadratus develops a pronounced outer lateral bulge when adult (figs. 116–118), while the umbilical bullae commonly migrate out to an inner flank position in middle and late growth.

Occurrence:

Widely distributed in the Western Interior in the upper Turonian Zone of Scaphites whitfieldi. Specimens have been found in south-central and southeastern Montana, central and eastern Wyoming, western South Dakota, eastern Utah, and over much of Colorado and New Mexico. It has also been recorded from Trans-Pecos Texas (Kennedy et al., 1989), and Tunisia (Amédro, 1990).

Types:

Holotype is USNM 108332 (fig. 103), paratypes USNM 108333a–c (figs. 104–106), from the upper Turonian Sage Breaks Member of the Carlile Shale in sec. 33, T. 9 S, R. 61 E, Carter County, Montana. Paratype USNM 108334 (fig. 102) is from a septarian concretion bed 12.8 m above the base of the Sage Breaks Member 14.5 km south-southeast of Rapid City in the NE¼ sec. 22, T. 1 S, R. 8 W, Pennington County, South Dakota. Paratype USNM 108335 is from a septarian concretion bed 5.2 m below the top of the Turner Sandy Member of the Carlile Shale 10.4 km north of Belle Fourche, in the E½ sec. 2, T. 9 N, R. 2 E, Butte County, South Dakota.

Diagnosis:

A fairly large species that has sparsely ribbed adult whorls with strong primary ribs and weak secondary ribs. Primary ribs on the robust form have umbilical bullae, nodate inner ventrolateral tubercles, and midflank swellings or weak tubercles. The gracile form usually lacks midflank swellings. No clearly defined outer ventrolateral tubercles occur on either form.

Description:

The types represent the robust form of the species. The holotype, USNM 108332 (fig. 103), is part of a small adult body chamber that has an intercostal width of 32.5 mm and height of 34.3 mm (ratio = 0.95) and a costal width of 42.0 mm and height of 38.2 mm (ratio = 1.10), with the greatest width at the umbilical shoulder. The specimen is an internal mold that does not have serrations on the keel preserved. A smooth ventral groove bounds the keel. Ribbing consists of strong, narrow, prorsiradiate primaries alternating with very weak, narrow secondaries. All ribs are straight on crossing the flanks, but they bend sharply forward on the ventrolateral shoulder and fade out on the venter. Primary ribs support umbilical bullae, weak midflank bullae, and blunt ventrolateral tubercles. Secondary ribs arise low on the flanks and efface on the venter without developing into ventrolateral tubercles.

A paratype, USNM 108334 (fig. 102), about 43 mm in diameter, has 42 ribs per whorl at a diameter of 30 mm with two or three secondaries separating primaries. At a larger diameter, most primaries are separated by a single secondary.

The suture figured by Cobban (1953: pl. 48, fig. 4) has a rather long lateral lobe, and a similar feature is shown in figure 107.

Discussion:

The species attains a large size, with some phragmocones having diameters of as much as 250 mm. Large specimens occasionally have blunt, nodate midflank tubercles. Keels are notched with more serrations than ribs.

The bulk of the specimens at hand represent the robust form. The gracile form tends to be more densely ribbed and lacks midflank swellings or bullae. Outer ventrolateral tubercles seem to be absent on both robust and gracile forms.

Occurrence:

Upper Turonian Scaphites nigricollensis and S. corvensis zones of the northern Great Plains of south-central and southeastern Montana and western South Dakota, and in equivalent strata in west-central New Mexico.

Type:

The lectotype, here designated, is the original of Reuss, 1845: 22, plate 7, figure 10, from the “Planermergel von Werschowitz.” The original figure is reproduced here as figure 109K.

Diagnosis:

Moderately to rather widely spaced, generally rounded, prorsiradiate ribs on the outer whorls characterize this species. Primary and secondary ribs tend to be of nearly uniform height. The keel is finely notched with many more serrations than ribs. The robust form has ribs that support bullate to nodate umbilical tubercles and nodate to clavate inner ventrolateral tubercles; weak outer ventrolateral clavi are present on some juveniles. The gracile form is weakly ribbed.

Description:

Robust and gracile forms can be recognized starting from very small diameters. In the juvenile robust form (fig. 113A–P, T, U), the coiling is fairly evolute, with the umbilical wall notched to accommodate the inner ventrolateral nodes of the preceding whorl; the umbilicus represents 36–38% of the diameter (table 12) with a flattened wall and broadly rounded umbilical shoulder. The intercostal whorl section is slightly compressed with the greatest breadth just outside the umbilical shoulder; the costal section is polygonal with the greatest breadth at the umbilical bullae. There are 16–24 ribs per whorl between 25 and 60 mm in most specimens. The ribs arise at the umbilical seam and bear well-developed umbilical bullae that migrate out to an inner flank position at as little as 20 mm diameter. These give rise to broad, blunt, crowded prorsiradiate ribs that are usually evenly developed, with only occasional irregularities. All bear feebly clavate to conical flat-topped inner ventrolateral tubercles that are the bases of long septate spines housed in grooves in the umbilical wall of the succeeding whorl, but rarely preserved (fig. 113X, Y). Low, broad, weakening ribs sweep forward and form an acute chevron with the line of the siphonal keel. Feeble outer ventrolateral clavi are present up to 15 mm diameter, but are thereafter lost, and the ribs are bituberculate. The strong siphonal keel is minutely and evenly crenulated. Larger specimens (figs. 113Q–S, V–Y, 114–118) vary in strength and coarseness of ribbing, with as few as 22 ribs of equal or unequal strength at 90 mm diameter, at which size the umbilical bullae migrate well out to the inner flank. This coarse, even or uneven ornament extends to the largest diameters seen.

The gracile form (figs. 109–112) has a whorl breadth to height ratio of 0.66–0.90 between 25 and 60 mm diameter (table 12). The coiling is evolute, with U = 35–40% of diameter; the umbilicus is shallow, with a low wall. Very crowded, even, primary ribs arise at the umbilical seam and strengthen across the flanks with no or only incipient bullae. Ribs are straight to feebly flexuous, and prorsiradiate on the flanks, where occasional long intercalated ribs yield a total of up to 70 ribs per whorl. Each rib bears a tiny conical to feebly clavate inner ventrolateral tubercle from which a weakening rib projects forward to form an acute ventral chevron with the minutely and evenly serrated siphonal ridge. Tiny outer ventrolateral clavi are present up to a diameter of approximately 10 mm, but are thereafter lost. From 60–150 mm this even style of ribbing continues, with around 36–40 ribs per whorl, which have feeble but variably developed umbilical bullae and inner ventrolateral clavi.

The suture is fairly simple, with a moderately deep lateral lobe (fig. 119).

Discussion:

Absence of an outer ventrolateral tubercle distinguishes this species from Prionocyclus wyomingensis when young, while the absence of an umbilical plus inner lateral tubercle separates it from P. wyomingensis when adult. The very even and sparser ribbing of P. germani alone serves to distinguish both juveniles and adults from P. novimexicanus. Prionocyclus quadratus generally has stouter quadrate whorls, and an incipient lateral tubercle when adult.

Ammonites schlönbachi Fritsch, 1872 (33, pl. 16, fig. 5) appears to be based on a poorly preserved crushed external mold of P. germari. A plaster cast taken from the mold, apparently the basis of the original figure, is shown as figure 108A. The flank ribs and long ventrolateral spines compare well with the Western Interior example shown in figure 113X, Y. Fritsch figured an undoubted juvenile P. germari from the same horizon and locality (1872: pl. 16, fig. 7).

Prionocyclus carvaholi Howarth, 1966 (p. 224, pl. 1, figs. 8–11; pl. 2, figs. 3–6; fig. 108D–F), from the Moçâmedes Desert, Angola, appears to be based on robust variants of the present species, even though Howarth (1966: 224) described very small “upper or inner ventrolateral tubercles … represented merely by a raised portion of the rib obliquely in front of the ventrolateral spine.”

Occurrence:

Fairly abundant at the top of the Frontier Formation in central Wyoming (Cobban, 1990), and in the D-Cross Tongue of the Mancos Shale in south-central New Mexico. The species is also present in the basal part of the Austin Chalk in the Rio Grande area of southwestern Texas, where it was reported as P. reesidei (Freeman, 1961). In all of these areas, P. germari is associated with Mytiloides incertus (Jimbo) and Eubostrychoceras matsumotoi Cobban of late Turonian, Scaphites corvensis/P. germari Zone age. The species also occurs in the upper Turonian of Germany, the Czech Republic, and Angola.

Derivation of Name:

Plurimus (Latin): most; costatus (Latin): ribbed.

Types:

Holotype is USNM 498491a (fig. 120D); paratypes USNM 498491b (fig. 120D), 498492 (fig. 120A), 498493 (fig. 120B), and 498494 (fig. 120C), all from USGS Mesozoic locality D11898, calcareous shale 4 m below the base of the Fort Hays Limestone Member of the Mancos Shale, upper Turonian, upper part of Prionocyclus germari Zone, NW¼, SE¼, sec. 22, T. 8 S, R. 87 W, Pitkin County, Colorado.

Diagnosis:

A densely and evenly ribbed Prionocyclus. There are up to 80 ribs per whorl in juveniles at 20 mm diameter, with inner ventrolateral clavi and outer ventrolateral clavi, if present, lost at a very early stage. Ribs may be single or arise in pairs or groups at the umbilical shoulder, or intercalate low on the flanks. Larger specimens with up to 90 ribs per whorl at 50 mm diameter, arranged as on nuclei, but bullate ribs bear strong inner ventrolateral clavi that are sometimes linked with weaker clavi or other ribs.

Discussion:

The types are crushed in shale, and there is little to add to the diagnosis. Prionocyclus pluricostatus n. sp. bears a superficial resemblance to P. bosquensis (fig. 76), also known only from crushed specimens in shales. They differ in that P. bosquensis has ribs of variable strength on nuclei, and persistent inner and outer ventrolateral tubercles. This last character separates the species from P. wyomingensis (see fig. 85A–C, F, G), whereas the eveness of ribbing separates it from P. macombi (fig. 67) and P. novimexicanus (fig. 88). P. germari (figs. 109, 113) has even ribbing, but specimens are never as densely ribbed as the present form. A specimen from New Mexico figured by Johnson (1903: 139, pl. 1, fig. 15) as Prionocyclus appears to be as densely ribbed as our species, but the New Mexico species is more involute.

The types occur with Mytiloides incertus at a very high level in the Turonian. We attribute them to the upper Turonian ammonite zone of P. germari, but they may represent a separate, as yet uncharacterized uppermost Turonian ammonite zone.

Occurrence:

As for types.

Type Species:

Prionocyclites mite Kennedy, 1988: 89, pl. 10, figs. 7–11; text-fig. 30.

Diagnosis:

“Inner whorls with distant bullate primary ribs separated by groups of weaker non-bullate primaries and occasional shorter intercalated ribs, all with a ventrolateral clavus. Keel broadly undulose, not serrated. Body chamber smooth but for distant bullate primaries and associated constrictions. Aperture constricted. Suture simple, with little-incised elements” (Kennedy, 1988: 89).

Discussion:

Prionocyclites is a progenetic dwarf, presumably derived from Prionocyclus, the inner whorls of the two sharing many common features (compare fig. 121 and fig. 51A–I), although the adult body chamber and simple adult suture of Prionocyclites are quite distinctive. It most closely resembles Lymaniceras Matsumoto, 1965, here interpreted as another progenetic dwarf collignoniceratid. However, Lymaniceras has a minutely serrated keel and lacks the Prionocyclus-like inner whorls and paucicostate, constricted body chamber of Prionocyclites (modified after Kennedy, 1988: 89).

Occurrence:

Prionocyclus hyatti Zone of north-east Texas only.

Type:

Holotype by monotypy in USNM 420144 (figs. 121, 122; Table 13) from the Arcadia Park Formation, Eagle Ford Group at USGS locality 22608 (ex Renfro Collection), east of power plant on Mountain Creek Lake, Dallas County, Texas; Prionocyclus hyatti zone.

Diagnosis:

Small species characterized by its arched venter and prominent keel. Ribs are sparse, conspicuously prorsiradiate, and bear oblique ventrolateral clavi.

Description:

“Holotype and only known specimen is a complete adult retaining traces of original shell. Coiling moderately evolute, with shallow umbilicus, umbilical wall low, rounded. Whorl section compressed with whorl breadth to height ratio 0.66. Flanks flattened, subparallel, with broadly round ventrolateral shoulders, venter with strong, blunt, undulose siphonal keel. On phragmocone there are twelve bullate ribs per whorl separated by two slightly weaker nonbullate ribs, giving a total of thirty-three to thirty-four ribs per whorl at the umbilical shoulder. Ribs are narrow, rounded, prorsiradiate, and straight on the inner flank, flexing forward and concave over the outer flank and ventrolateral shoulder. A few short ribs intercalate on the outer flank and all ribs bear a blunt, obliquely placed ventrolateral clavus. The ribs project forward from the clavus towards the mid-line of the venter but decline before reaching the keel. The low undulations on the keel do not correspond to the ribs; they are far fewer in number. This ornament extends on to the first part of the body chamber but thereafter rapidly declines. The last part of the body chamber is near-smooth between three very distant ribs that arise from prominent umbilical bullae. These ribs are narrow, rounded, and efface by the ventrolateral shoulder. They are followed by a shallow constriction, most obvious at the ventrolateral shoulder. A much stronger constriction marks the adult aperture. Suture very simple with broad, little-incised E/L and narrower L; not approximated at the end of the phragmocone” (Kennedy, 1988: 89).

Discussion:

The only ammonites with which Prionocyclites mite Kennedy, 1988, is likely to be confused are species of Lymaniceras Matsumoto, 1965. The type species, L. planulatum Matsumoto, 1965 (31, pl. 6, figs. 1, 2; pl. 7, figs. 1–5; pl. 8, figs. 1–8; text-figs. 10–16), is also a progenetic dwarf, but without the distinctive differentiation of primary ribs seen in Prionocyclites and with a finely serrated keel. Body chambers are very different.

Occurrence:

As for type.

Type Species:

By original designation: Barroisiceras minimum (Yabe ms.) Hayasaka and Fukada, 1951: 325, pl. 1, figs. 1–4; pl. 2, figs. 1–7.

Diagnosis and Discussion:

See Matsumoto, 1965: 61.

Occurrence:

Upper Turonian, Japan, Tunisia, Armenia, Colombia, and New Mexico in the U.S. Western Interior.

Type:

Holotype, by original designation, is the original of Hayasaka and Fukada, 1951: 326, pl. 4, figs. 1–4, from the Upper Turonian of the Ikushumbets, region Hokkaido, Japan.

Diagnosis:

A compressed, involute species that attains a diameter of about 100 mm. The narrow cross section has flattened convergent and fastigiate venter with sharply defined ventrolateral shoulder. Ornament of low, broad, somewhat flexuous primary and secondary ribs, each supporting a low ventrolateral clavus and terminating in a midventral clavus. Primary ribs begin from low umbilical bullae.

Description:

The smaller specimen, USNM 414511 (fig. 123A, B) is wholly septate. Coiling is very involute with an umbilicus to diameter ratio of 0.12; the umbilical wall is somewhat flattened. The whorl section is very compressed, with a whorl breadth to height ratio of 0.52, the greatest breadth at the umbilical bullae; the costal whorl section has flattened, convergent sides and a fastigiate venter. There are three distant umbilical bullae per half whorl. These give rise to pairs of low, broad, prorsiradiate ribs that are flexed back on the outer flanks. They strengthen across the flanks, and additional intercalaries arise low on the flanks to give a total of 13 ribs per half whorl. All ribs bear ventrolateral clavi and strong siphonal clavi on the crest of the fastigiate venter so that the shell has a strongly crenulate margin when viewed from the side.

The larger specimen, USNM 414510 (fig. 123C, D), is crushed, and preserves half a whorl of body chamber; it appears to be a nearly complete adult with the umbilical seam egressing markedly around the last half whorl. There are five umbilical bullae on the last half whorl of the phragmocone, corresponding to 18 ribs at the ventrolateral shoulder. The ribs arise in pairs from bullae. There are both long and short intercalaries and all are commonly flexed back and convex around midflank. All ribs terminate in ventrolateral clavi. The siphonal clavi are very prominent. On the body chamber the whorl section broadens somewhat and the venter rounds. The umbilical bullae decline and eventually disappear; most of the ribs are long, extending to the umbilical shoulder as both ribs and striae, while prominent growth lines develop. The ventrolateral and siphonal tubercles decline markedly towards the aperture.

The suture line has a markedly asymmetric, bifid E/L, the ventral half smaller than the dorsal; rectangular L that is deeper than E; asymmetrically bifid L/U₂; and relatively broad and bifid U₂ (fig. 124).

Discussion:

The larger, crushed specimen closely resembles the holotype, whereas the smaller matches that figured by Obata (1965: pl. 5, fig. 5). Reesidites elegans Matsumoto and Inoma, 1971 (in Matsumoto, 1971: 139, pl. 23, figs. 1–3; text-figs. 5–7) has much finer, more numerous, delicate, and weaker ribs than R. minimus. R. latus Matsumoto and Obata (1982: 82, pl. 6, fig. 2) is much more evolute, with U/D = 0.40 at maturity and a broader whorl. R. subtuberculatus (Gerhardt, 1897: 156, pl. 3, fig. 12) has much weaker flank ornament and tubercles.

Occurrence:

Scaphites ferronensis/Prionocyclus wyomingensis Zone of Valencia County, New Mexico and Scaphites whitfieldi Zone of Socorro County, New Mexico; upper Turonian of Japan, Austria, Tunisia, and Armenia.