NO. 3 CASSIDULOID ECHINOIDS — KIER 93 



of P. coxwellense Melville or of P. farhigdoncnse. The posterior 

 ocular plates are very large in P. olfersii (text fig. 74), and it is prob- 

 able that d'Orbigny mistook one of them for a supplementary plate. 



Synonyms of PLAGIOCHASMA 



Dochmostoma Duncan, 1891. Journ. Linn. Soc. (Zool.), vol. 23, p. 176. Type 

 species herein designated, Nncleolitcs olfersii L. Agassiz. 



Remarks. — Dochmostoma is a junior objective synonym of Plagio- 

 chasma, both genera having the same type species. Duncan created 

 this genus because he did not like the name Trematopygus. 



Trematopygus d'Orbigny, 1857. Pal. franc, Cretace, vol. 6, p. 374; non Holm- 

 gren (185s, K. Svensk. Vetensk. Akad. Handl., N. F., vol. i, p. 179; a genus 

 of Hymenoptera) . Type species : Nncleolitcs olfersii Agassiz by subsequent 

 designation, Lambert and Thiery (1921, p. 338). 



Genus OOLOPYGUS d'Orbigny 



Oolopygus d'Orbigny, 1856. Pal. franc, Cretace, vol. 6, atlas, pis. 976-977. 

 Type species, Oolopygus gracilis 'La.mhcrt=:Oolopygt{s pyriformis d'Orbigny 

 1856, non Oolopygus pyriformis (Leske, 1778), by subsequent designation, 

 Cotteau (m d'Orbigny i860, p. 458). 



Synonym: ? Pseudonucleus Lambert. 



GENERIC DESCRIPTION 



Small to medium size, elongate, with or without pointed posterior 

 margin, inflated, with steep sides; apical system tetrabasal, anterior, 

 three or four genital pores (no pore in genital 3 in some species), 

 petals slightly developed, flush, equal, often difficult to discern, pores 

 of pore pair equal, or outer elongated transversely, ambulacral plates 

 beyond petals single pored ; periproct marginal, longitudinal, often with 



Figs. 73-80. — 73, Plagiochasma cxccntricus (Pictet and Renevier) : Phyllode 

 of ambulacrum II from specimen in De Loriol Collection, at the I^Iuseum 

 d'Histoire Naturelle, Geneve, Switzerland, from the Lower Cretaceous (Aptian) 

 at Boveresce (Neuchatel), Switzerland, X I5- 74-75, Plagiochasma olfersii 

 (Agassiz) : 74, Apical system of specimen in Roman Collection from the 

 Lower Cretaceous (Hauterivian), at Devecey (Doubs), France, XiS; 75. 76, 

 adoral plate arrangement (X2) and phyllode of ambulacrum V (X I5) of 

 USNM 21814, from Lower Cretaceous (Neocomian) at St. Croix, Switzerland. 



77, Oolopygus gracilis Lambert : Phyllode of ambulacrum V of Lambert's 

 (1900, pi. I, figs. 17-18) figured specimens in the Lambert Collection, Sorbonne, 

 Paris, from the Upper Cretaceous (Maestrichtian), Fresville, France, X I5- 



78, Oolopygus pyriformis (Leske) : Phyllode of ambulacrum I of Lambert's 

 figured specimen in the Lambert Collection, Sorbonne, Paris, from the Upper 

 Cretaceous (Maestrichtian) at Fresville (Manche), France, X I5- 79> 80, Pseu- 

 donucleus malladai Lambert : 79, Apical system of holotype in Lambert Collec- 

 tion, Sorbonne, Paris, from the Upper Cretaceous (Campanian) of Roiz, San- 

 tender, Spain, X21 ; 80, phyllode of ambulacrum III of same specimen, X 21. 



