ECHINODERMA. ECHINOIDEA 



131 



Echinocorys ( = Ananchytes) (fig. 47 B). Test very convex 

 above, inferior surface flattened, outline oval. Apical disc a little 

 elongated ; the four genital plates perforated, the two anterior sepa- 

 rated from the two posterior by two large ocular plates. Ambulacra 

 simple, pores unigeminal. Interambulacral plates large, tubercles 

 small. Peristome anterior. Periproct oval, infra-marginal. Upper 

 Chalk. Ex. E. vulgaris. 



Fig. 52. Holaster subglobosus, Chalk. Upper and lower surfaces. 



V 2 



x - s . 



Holaster (fig. 52). Test heart-shaped, inferior surface more 

 or less flattened, superior surface with a broad shallow groove 

 in front. Apical disc elongate, the two pairs of genital plates 

 separated by two oculars. Ambulacra large, simple ; pores uni- 

 geminal, round or elongate ; the anterior ambulacrum in the groove. 

 Interambulacra with small tubercles and granules. Peristome near 

 the anterior margin, elliptical. Periproct supra-marginal. Upper 

 Greensand and Chalk ; also Tertiary in Australia. Ex. H. sub- 

 globosus, Lower Chalk. 



Cardiaster. Form similar to Holaster, but anterior groove 

 usually with sharp borders. Apical disc similar to Holaster. Pores 

 elongate, unigeminal. Small perforate and crenulate tubercles. 

 Peristome near the anterior margin, with a projecting lip. 

 Periproct on the posterior truncated end. Fasciole passes beneath 

 the periproct and round the margin of the test. Cretaceous. Ex. 

 C. ananckytis, Chalk, 



9—2 



