NO. 3 CASSIDULOID ECHINOIDS — KIER 165 



Range and distribution. — Upper Cretaceous (Cenomanian to Mae- 

 strichtian) of Europe, Africa, and United States. Lambert and 

 Thiery give a much wider range to this genus, from the Aptian to 

 Recent. However, the Aptian species, Desor's Echinobrissus placen- 

 tula, is not a Nucleopygus. I have seen specimens of this species; 

 its phyllodes are double pored and it should be referred to Nucleo- 

 Utes. The oldest specimens I have seen of Nucleopygus were from 

 the Cenomanian, Gres Vert, at Le Mans. These specimens, which 

 are in the ficole National Superieure des Mines in Paris, were labeled 

 Niicleolites lacunosus but resemble more closely d'Orbigny's Echino- 

 brissus similis. They have single-pored phyllodes and definitely be- 

 long in Nucleopygus. A photograph of the adapical surface of one 

 of them is included herein (pi. 24, fig. 9). I have also seen speci- 

 mens of Agassiz's Niicleolites parallelus from the Turonian, and 

 d'Orbigny's Echinobrissus minimus from the Senonian. Both of 

 these species have single-pored phyllodes (text figs. 138, 139) with 

 very few pores, small tests, slightly developed petals, and a supra- 

 marginal periproct, all characters typical of Nucleopygus. Of the 

 three post-Cretaceous species that Lambert and Thiery refer to 

 Nucleopygus, Edwards' Nucleolites recens is the type species of 

 another genus, Apatopygus; Cotteau's Echinobrissus dclfortrieri and 

 Zittel's Nucleolites papillosus may each be a Cassidulus. 



DESCRIPTION OF TYPE SPECIES 



NUCLEOPYGUS MINOR Desor 

 Plate 24, figures 10, 11; text figure 140 

 Nucleopygus minor Desor, 1842. Des galerites, p. 33, pi. 5, figs. 20-22. 



Material. — Nine specimens studied in the Lambert Collection at 

 the Sorbonne, one in the Museum National d'Histoire Naturelle, 

 Paris, and three in the Museum of Comparative Zoology, Harvard. 



Shape. — Very small, usually less than 8 mm. long, moderately 

 inflated with greatest height anterior to center, greatest width pos- 

 terior ; anterior margin smoothly rounded, posterior slightly truncated 

 by anal groove; sides smoothly rounded, adoral surface depressed 

 at peristome. 



Apical system. — Anteriorly eccentric, tetrabasal, with four genital 

 pores. 



Ambulacra. — Petals inconspicuous, narrow, open, flush with test, 

 short, petal HI shorter than others, inner pore of pore pair round, 

 outer round or slightly elongate transversely, conjugate. 



