ECHINODERMA TA—ECHINOIDEA . 



585 



IX. Pholidocidaris Meek and Worthen. 



With coarse, highly irregular, imbricating interambulacral plates, 

 of which it has five or more columns ; and six or more columns 

 of irregular, much smaller ambulacral plates ; large spines at scat- 

 tered intervals. Distinguished from Lepidechinus by the much 

 greater breadth of its ambulacral areas, by its more numerous rows 

 of ambulacral pieces and pores and by larger size. Mississippic. 

 17. P. irregularis Meek and Worthen. Mississippic. 



Marginal interambulacral plates large, elliptical, each bearing a 

 cylindrical spine about one inch long; number of columns 5-6; 

 ambulacral plates most irregular in size, increasing in size and 

 <lecreasing in number towards end of area. 



Keokuk of Illinois. 



Subclass Euechinoidea Bronn. 



Order CIDAROIDA Duncan. 



X. CiDARis Klein. 



Test spheroidal. Mouth opening central below. Anal opening 



subcentral above. Ambulacra narrow, undulating, extending from 



top to bottom and composed of very numerous plates. The pairs 



of pores are arranged in a single series, the two pores of each pair 



rather close and separated by a small knob or ridge. Primary 



tubercles perforated and crenulated. Permic-Recent. 



Fig. 1918. Cidaris texana. «, test restored, X K 5 ^' interambulacral plate en- 

 larged ; c, tubercle much enlarged ; d, portion of ambulacral area enlarged. (After 

 Clark.) 



