QO SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I44 



Plagiochasma is also very similar to Pygopistes, both genera hav- 

 ing similar petals, oblique peristome, and similar floscelle. However, 

 in Plagiochasma the test is lower, and the periproct is supramarginal. 



Lambert and Thiery (1921, p. 339) include among the species they 

 refer to Trematopygus (= Plagiochasma), Fourtau's (191 3, p. 62) 

 Trematopygus aegyptiacus. Fourtau (1921, p. 62) later transferred 

 this species to Botriopygus. It is certainly not a Plagiochasma as 

 shown by its marginal to inframarginal periproct, and monobasal 

 apical system, but probably is a Parapygns. Fourtau in this same 

 work described a Plagiochasma, P. sinaeus (Fourtau) from the 

 Cenomanian of Egypt. 



Lambert and Thiery referred Clark's Echinobrissiis texanus from 

 the Coniacian Austin Chalk of Texas to Trematopygus {= Plagio- 

 chasma). Later, Cooke (1953, p. 13) placed this species in Nucleo- 

 pygtis. I have studied the holotype and agree with Lambert and 

 Thiery that the species is a Plagiochasma. Its shape, petal arrange- 

 ment, position of periproct, and phyllodes are typical of that genus. 

 Apparently its peristome is also oblique, but this area is not well 

 preserved on the holotype. Its phyllodes are definitely double pored 

 and very similar to those of P. olfersii whereas in Nucleopygus they 

 are single pored. 



I studied a specimen of Plagiochasma excentricus (Pictet and 

 Renevier) in the De Loriol Collection at the Museum d'Histoire 

 Naturelle in Geneve, Switzerland, and include a drawing (text fig. y^i) 

 of one of its phyllodes. It is of interest to note that the phyllode 

 is slightly widened, whereas in P. olfersii the outer pore series is 

 straight. 



Melville (1952) described a new species of Plagiochasma, P. cox- 

 wellense, from the Aptian, Lower Greensand in England, including 

 several excellent, detailed drawings of the plate structure. Zazvorka 

 (1953) reported a new species, Plagiochasma vovaki (Zazvorka), 

 from the Lower Turonian of Bohemia. 



Range and distribution. — Cretaceous (Neocomian to early Seno- 

 nian) of Europe, Egypt, and the United States. 



DESCRIPTION OF TYPE SPECIES 



PLAGIOCHASMA OLFERSII (L. Agassis) 



Plate 14, figures 1-3; text figures 74-76 



Niicleolites olfersii L. Agassiz, 1836a. Mem. Soc. Sci. Nat. Neuchatel, vol. i, 

 p. 133, pi. 14, figs. 2, 3. 



Material. — Sixteen specimens studied in the Museum of Compara- 

 tive Zoology, Harvard, two in the d'Orbigny Collection at the Museum 



