ECHINODERMA TA—ECHINOIDEA . 



589 



XV. Cyphosoma Agassiz. 



Test depressed, highly ornamented. Ambulacra with well- 

 developed pore-bearing zones, undulating, and each plate with three 

 to seven pairs of pores in an arc. Pairs of pores in two rows at 

 the apex and crowded at the mouth opening. Interambulacra with 

 two or more vertical rows of primary tubercles which are imper- 

 forate and crenulate, like those of the ambulacra. Apical system 

 encroaching upon the posterior interambulacrum. Jurassic-Recent. 



23. C, volanum Cragin. Comanchic. 



Small, similar in form to Pseudodiadema texanum; pore belts 

 sinuous; ambulacral area with two vertical rows of primary tuber- 

 cles, surrounded by narrow strings of granules in polygons ; inter- 

 ambulacral area with two rows of large primary tubercles, with a 

 row of smaller ones on either side of the area. 



Upper Washita of Texas. 



Order HOLECTYPOIDA Duncan. 



XVI. HoLECTYPUS Desor. 



Ambulacra narrow, straight, widest at the ambitus ; some of the 

 plates compound. Interambulacra with rather large plates and 



Fig. 1922. Holectypus planalus. a, lower, b, upper, c, posterior view ; d, 

 ambulacral plates much enlarged ; <?, apical system enlarged. (After Clark.) 



