ORDER II 



EUECHINOIDEA DIADEMATOIDA 



231 



Sub-Family D. ORTHOPSIXAE. 



Ambulacra with simple primary plates ; pairs of pores in simple series. 

 Orthopsis, Cott. Amb much narrower than the I Amb, straight, and with 

 numerous pairs of pores in straight series. Amb with two, lAmb with several 

 vertical rows of small, plain, perforate tubercles. Jura and Cretaceous. 



Eodiadema, Duncan. Lias ; England. Echmopsis, Ag. Eocene ; Europe 

 and Egypt. 



Family 4. Cyphosomatidae. 



Test highly ornamented, moderate in size. Ambulacra with high compound plates, 

 each with three to seven pairs of poi'es in an arc; the pairs sometimes biserial near 

 the apical system, and crowded near the peri- 

 stome. The adoral and supra-adoi-al com- 

 ponents of the plates are primaries, and the 

 others demi-plates. Ambulacra with two 

 vertical rows of primary tubercles ; interam- 

 Imlacm with a variable number. Jura to 

 Recent. 



Cyphosoma, Ag. (Fig. 371). Test de- 

 pressed, with few coronal plates. Amb' 

 with well-developed poriferous zones, 

 undulating. Pairs of pores biserial at 

 the apex, crowded at the peristome. 

 Limb broader than the Amb, with two or 

 more vertical rows of primary tubercles, 

 which are imperforate and crenulate, 

 like those of the Amb. Apical system 

 encroaching upon the posterior I Amb. 

 Jura to Recent. 



Micropsis, Cott. Amb with three to five pairs of pores to a compound 

 plate, and two or more vertical rows of small primary 

 tubercles, which are perforate and crenulate. Cretaceous 

 and Eocene. 



Family 5. Arbaciidae. Gray 



Test depressed dor sally, flat actinally. Ambulacra narrow, 

 straight, expanding near the peristome, with compound plates 

 near the ambitus. Pairs of pores simple or in large arcs, 

 sometimes crowded actinally. Interambulacra with few or 

 several vertical rows of imperforate, non-crenulate, primary 

 tubercles with expanded bosses. Tertiary and Recent. 



Arbacia, Gray. Tertiary and Recent. Echinocidaris, 

 Duncan and Sladen (non Desmoulins). Recent. 

 . . , Goelopleurus, Ag. (Fig. 372). Amb with two vertical 



Eocene ; Biarritz. France. J/i. t i , i 11 i a i i 



1 rows of plain, primary tubercles placed on flat scrobicules, 

 diminishing in size toward the apex, and sometimes replaced there by granules. 

 lAmb with a large bare median area abactinally ; the tubercles largest at the 



Fw. 371. 



Cyphosoma Koenigi, Mantell. White Chalk ; 

 Sussex. Ventral aspect, Vi- 



Fio. 372. 

 Coelopleurus equis, 



