586 



NORTH AMERICAN INDEX FOSSILS. 



1 8. C. texana Clark. (Fig. 19 18.) Comanchic. 



Test large. Ambulacral areas with four rows of granules be- 

 tween the pore-bearing zones on the under side, increased to six 

 at the ambitus and reduced to two at the apex. Pores oval, sepa- 

 rated by transverse ridges which partially envelop the openings. 

 Areolas circular, depressed. 



Washita of Texas. 



XI. Leiocidaris Desor. 

 Test large, swollen. Differs from Cidaris in having the two 

 pores of each pair distant and united by a groove. Tubercles 



Fig. 19 19. Leiocidaris hemigranosa, upper and lateral views, x %> 

 (After Clark.) 



large, not crenulated. Spines large, smooth, cylindrical. Cretacic- 



Recent. 



19. L. hemigranosa (Shumard). (Fig. 1919.) Comanchic. 



Ambulacral areas with six rows of granules in the middle. Pore- 

 bearing zones deeply depressed. 



Denison (Washita) of Texas. 



Order DIADEMATOIDA Duncan. 



XII. Diadem A Schynvoet (includes Pseudodiadema Desor). 



Test highly ornamented. Ambulacra straight, with two vertical 

 rows of small primary perforate and crenulate tubercles extending 

 from mouth to apex. Pairs of pores in simple vertical series or in 

 arcs of threes. Interambulacra with two or more vertical rows of 



