The New World genus Cathorops in the family Ariidae (Sea Catfishes) includes species that inhabit estuarine and coastal waters as well as freshwaters, playing an important role in Neotropical coastal and estuarine fisheries. The relatively conserved external morphology coupled with the marked sexual dimorphism and ontogenetic variation makes it difficult to recognize and diagnose the species. One of the major problems concerns the nomenclatural and geographical limits of C. spixii, described from tropical Brazil and often treated as the only coastal marine species in the genus from the Western Atlantic. Examination of types of nominal species as well as comprehensive collections of non-types from Caribbean and Atlantic South America, lead us to conclude that C. spixii is restricted to Brazil and that C. nuchalis is a valid species, ranging from Venezuela to Guyana. The nominal species Arius laticeps, Arius nigricans, and Arius variolosus are synonyms of C. nuchalis, C. spixii, and C. arenatus, respectively. We also describe a new species in the Cathorops mapale species group from Colombia and Venezuela.