ORDER II EUECHINOIDEA—DIADEMATOIDA 231 
Sub-Family D. ORTHOPSINAE. 
Ambulacra with simple primary plates ; pairs of pores in simple series. 
Orthopsis, Cott. dmb much narrower than the Ld4mb, straight, and with 
numerous pairs of pores in straight series. Amb with two, L4mb with several 
vertical rows of small, plain, perforate tubercles. Jura and Cretaceous. 
Eodiadema, Duncan. Lias; England. Lchinopsis, 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 pores in an arc, the pairs sometimes biserial near 
the apical system, and crowded near the peri- 
stome. The adoral and supra-adoral com- 
ponents of the plates are primaries, and the 
others demi-plates. Ambulacra with two 
vertical rows of primary tubercles ; interam- 
bulacra with a variable number. Jura to 
Recent. 
Cyphosoma, Ag. (Fig. 371). Test de- 
pressed, with few coronal plates. dmb 
with well-developed poriferous zones, 
undulating. Pairs of pores biserial at 
the apex, crowded at the peristome. 
IAmb 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 a. “i oy dep 
encroaching upon the posterior [4mb. Ree ee eae WEEE: 
Jura to Recent. 
Micropsis, Cott. dmb 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 Kocene. 

Fic. 371. 
Family 5. Arbaciidae. Gray 
Test depressed dorsally, flat actinally. Ambulacra narrow, 
straight, expanding near the peristome, with compound plates 
near the ambitus. Pairs of pores simple or in large ares, 
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. LHchinocidaris, 
Fi. 872. Dunean and Sladen (non Desmoulins). Recent. 
Coeloplewrus equis, Ag. Coeloplewrus, Ag. (Fig. 372). Amb with two vertical 
Eocene; Biarritz, France. 1/;. Aid ci 
ocene; Biarritz, Franee. T/- pows of plain, primary tubercles placed on flat scrobicules, 
diminishing in size toward the apex, and sometimes replaced there by granules. 
IAmb with a large bare median area abactinally ; the tubercles largest at the 
