The Bostryx stelzneri species complex is taxonomically reviewed with the description of a new species. This complex is formed by Bostryx stelzneri (Dohrn, 1875), B. peristomatus (Doering, 1879), B. scaber (Parodiz, 1948) and Bostryx roselleus n. sp., all distributed in Argentina. Bostryx peristomatus and B. scaber are elevated to specific status on the basis of morphological characters. This complex has the spire less than half the total shell height and the aperture higher in relation to total shell height than in any other species of the genus. Traditional shell morphometry and a geometric morphometric analysis were used to document shell variation in size and shape among species. Radula, jaw and shell morphology were examined with SEM. All species in the complex are described or redescribed using new morphological information. In this species complex, pallial organs are very similar among species and vary only in the degree of opening of the secondary ureter. The genitalia differ in the relative proportion of organs, such as length of vagina relative to free oviduct and penis or epiphallus length relative to penis length. Sculpture of the inner wall of the flagellum and epiphallus is similar in all species studied, whereas sculpture of the inner wall of the penis is variable. Geometric morphometric analysis allows an objective interpretation of shell shape variation detecting differences in shape components irrespective of the differences in size between Bostryx Troschel, 1847 species of the stelzneri group.