130 ECHINODERMA. ECHINOIDEA 



more elevated. Apical disc elongated — the two anterior genitals 

 separated from the two posterior by two oculars. Ambulacra simple, 

 pores unigeminal. Interambulacra wide. Tubercles very small. 

 Periproct next the apical disc, in a long groove on the dorsal surface. 

 Peristome a little in front of the centre. Inferior Oolite to Coral- 

 lian. Ex. H. gibbemhcs, Inferior Oolite. 



Nucleolites ( = Echinobrissus). Test depressed ; outline oval 

 or quadrilateral, rounded anteriorly, truncated and broadest poste- 

 riorly ; inferior surface concave. Apical disc compact, four perforate 

 genital plates, and one imperforate. Ambulacra sub-petaloid, pores 

 unigeminal, the outer pore elongated in the sub-petaloid part. 

 Interambulacra] plates wide, tubercles small. Peristome oval or 

 pentagonal, excentric, a little anterior. Periproct placed in a sulcus 

 on the dorsal surface. Inferior Oolite to present day. Ex. N. scu- 

 tatus, Corallian. 



Clypeus. Test large, flattened, more or less discoidal, with 

 circular or pentagonal outline, and flat or concave base. Apical disc 

 small. Ambulacra large, petaloid, pores unigeminal (except near the 

 peristome), outer pore elongated and in a long groove. Peristome 

 nearly central, with a floscelle. Periproct on the dorsal surface, 

 often in a sulcus. Tubercles very small. Inferior Oolite to Corallian. 

 Ex. C. ploti, Inferior Oolite. 



CatopygUS. Test small, oval, elevated, truncated behind, 

 with flat base. Apical disc small. Ambulacra sub-petaloid, uni- 

 geminal, outer pore elongated in the sub-petaloid parts. Tubercles 

 very small. Periproct high up on the posterior end. Peristome a 

 little excentric, small, with a floscelle. Cretaceous to present day. 

 Ex. C. colwnbarius, Upper Greensand. 



Collyrites (fig. 47 C). Test ovoid, inflated. Apical disc 

 greatly elongated ; at the anterior end are four perforated genital 

 plates separated by two oculars, at the posterior end are two oculars ; 

 these two groups of plates are connected by numerous small plates. 

 Ambulacra simple, pores unigeminal. The three anterior ambulacra 

 meet at the anterior end of the apical disc, the other two meet at 

 the posterior end. Interambulacra broad, tubercles small. Peri- 

 stome excentric. Periproct above the posterior margin. Upper Lias 

 to Cretaceous. Ex. C. bicordata, Corallian. 



