Crotoclypeus differs from Clypeus in having its periproct well-separated from the apical disc, with or without catenal plates linking the apical disc and periproct. It is therefore exocyclic, while Clypeus is endocyclic. The test is consistently taller than that of Clypeus.
Crotoclypeus is similar to Dactyloclypeus. Maccagno erected Dactyloclypeus as a new subgenus of Clitopygus (considered by Kier (1962) to be a synonym of Nucleolites). Dactyloclypeus is closer morphologically to Clypeus than Nucleolites. In erecting a subgenus of Clitopygus, Maccagno may have been referring to the work of Lambert & Thiery (1925, p. 586), who synonymised Clitopygus with Crotoclypeus on the basis of the position of the periproct.
According to Kier (1962, p. 35) the presence of catenal plates joining the apical system to the periproct appears to be variable within the genus and even the type species.
Pomel, A. 1883. Classification méthodique et genera des Échinides vivante et fossiles. Thèses présentées a la Faculté des Sciences de Paris pour obtenir le Grade de Docteur ès Sciences Naturelles, 503, 131 pp. Aldolphe Jourdan, Alger.
P. M. Kier 1962. Revision of the cassiduloid echinoids. Smithsonian Miscellaneous Collections 144 (3) 262 pp.
Barras, C. G. 2006. British Jurassic irregular echinoids. Monograph of the Palaeontographical Society no. 625 (part of volume 159 for 2005), 1-168, pls 1-14.