86 SMITHSONIAN MISCELLANEOUS COLLECTIONS VOL. I44 



apical system very eccentric anteriorly, tetrabasal, four genital pores ; 

 petals long, extending almost to margin, open, narrow poriferous 

 zones, tapering distally, pores conjugate, outer elongate transversely ; 

 all ambulacral plates double pored ; periproct marginal, elongate longi- 

 tudinally; peristome anterior, oblique, large, depressed; bourrelets 

 slightly developed; phyllodes slightly broadened, double pored, two 

 series of pore pairs in each hal f -ambulacrum ; no buccal pores, no 

 naked sternal area. 



Comparison zvith other genera. — Lambert and Thiery (1921, p. 

 340) and Mortensen (1948, pp. 141, 143) consider Pygopistes as a 

 synonym of Pygorhynchiis. However, the two genera are quite 

 distinct. In Pygopistes the test is much more inflated, with steeper 

 sides, a more rounded marginal outline and a more pulvinate adoral 

 surface. The apical system is much more eccentric anteriorly in 

 Pygopistes, and there are fewer pore pairs in the phyllodes. 



The type species of Pygopistes and Plagiochasma are very similar, 

 both having an oblique peristome, similar phyllodes and petals, but 

 they differ in that in Pygopistes coquandi the test is more inflated, 

 and the periproct is marginal. Pygopistes differs from Pygaulus in 

 having a more anteriorly eccentric apical system, and a more highly 

 inflated test. 



Range and distribution. — Cretaceous (Cenomanian) of North 

 Africa. 



DESCRIPTION OF TYPE SPECIES 



PYGOPISTES COQUANDI (Cotteau) 



Plate 13, figures 1-6; text figure 71 



Pygaulus coquandi Cotteau, 1869, Rev. Mag. Zoo!., ser. 2, vol. 21, pp. 243-245, 

 pi. 13, figs. 1-4. 



Material. — Specimens were studied in the De Loriol Collection 

 at the Museum d'Histoire Naturelle at Geneve, in the Cotteau Col- 

 lection at the ficole des Mines, Paris, and in the Museum National 

 d'Histoire Naturelle, Paris. 



Shape. — Small, 25 mm. long, elongate, marginal outline smoothly 

 rounded, right anterior margin slightly prolonged, extending farther 

 anteriorly than left anterior margin, right posterior margin slightly 

 more prolonged than left; test highly inflated, in some specimens 

 greatest height anterior to center, in others near center; adoral 

 surface slightly pulvinate with phyllodes and peristome slightly 

 depressed. 



