ECHINODERMATA. 285 



Family DIADEMATIDAE. 



Genus PsEudodiadsma Desor. 



Pseudodiadema diatretum (Morton). 



Plate IX., Figs. 1-6. 



1833. Cidaris diatretum MoTt., Am. Jour. Sci., ist ser., vol. 23, 



p. 294. 



1834. Cidarites diatretum Mort., Synop. Org. Rem. Cret. Gr. 



U. S., p. 75, pi. 10, fig. 10. 



1858. Pseudodiadema diatretum Desor, Synop. des Echin. 



Foss., p. 73. 



1859. Cidaris diatretum Gabb, Cat. Inv. Foss. Cret. Form. U. 



S., p. 18. 

 1864. Pseudodiadema diatretum Meek, Check List Inv. Foss. 



N. A., Cret. and Jur., p. 2. 

 1868. Pseudodiadema diatretum Con., Cook's Geo!, N. J., p. 



722. 

 1870. Cidaris clazngera and Cidaris sceptrifera Credner, Zeitsch. 



d. Deutsch. Geol. Gesell., vol. 22, p. 218. 

 1 89 1. Pseudodiademoi diatretum, Clark, Johns Hopkins Univ. 



Circ, vol. 10, No. 87, p. 75. 

 1893. Pseudodiadema diatretum Clark, John Hopkins Univ. 



Circ, vol. 12, No'. 103, p. 51. 

 1893. Pseudodiadema diatretum, Clark, Bull. U. S. G. S., No. 



97. p. 46, pi. 13, figs. I a-f. 

 1905. Pseudodiadema diatretum Johns., Proc. Acad. Nat. Sci. 



Phil., 1905, p. 6. 



Description. — Test circular, depressed, concave below, the sides 

 inflated, the dorsal surface slightly convex. Ambulacral areas 

 wide, slightly raised, with two rows of 13 or 14 tubercles each, 

 which are lai-ge and prominent at the ambitus, and decrease 

 gradually towards the poles ; the areolas broad, sharply depressed 

 in their marginal portion, and marked by fine radial ridges on the 

 outer sides ; at the upper and inner angle of each plate is a small 

 secondary tubercle, while scattered over the other portions of the 

 plates are smaller tubercles, and between them minute granules; 



