ECHINOIDEA. 241 



Moreover, the ambulacral zones are expanded and petaloid 

 in the immediate neighbourhood of the mouth, and so form 

 an " oral rosette " in the centre of the base, while the tuber- 

 cles are often perforated. Of the more important genera of 

 this family, Pygurus is Oolitic and Cretaceous, Conoclypus 

 and Echinanthus are Cretaceous and Tertiary, and Echino- 

 lampas is Tertiary and Recent. 



In the family of the Clypeastridce the test is usually 

 circular or elliptical, generally depressed, the surface covered 

 with small tubercles surrounded by sunken, ring-like arcolce, 

 and carrying hair-like spinqs. The dorsal portions of the 

 ambulacral zones are wide and petaloid, and the ambulacral 

 pores are confined to the apical " rosette " thus formed. The 

 mouth is inferior, central, and armed with teeth ; and the 

 anus is marginal or infra-marginal. The numerous types 

 included in this family range from tho Cretaceous to the 

 present period, the most important genera being Clypeaster, 

 Scutella (fig. 120), Echinocyamus, and Echinarachnius. 



In the family of the Ananchytidce ( = Echinocoridce, Wright) 

 the test is usually ovate or heart-shaped, the mouth is tooth- 

 less, excentric, and advanced forward, and the anus is mar- 

 ginal, infra-marginal, or supra-marginal (fig. 137, B). The 

 ambulacral areas are not petaloidal, and the ambulacral pores 

 are not confined to a dorsal rosette. There are four genital 

 pores in the apical disc ; the tubercles are small, perforated, 

 and crenulated ; and the spines are minute. 



The chief genus of this family is Ananchytes itself (fig. 

 137, B), represented by many forms in the Cretaceous rocks. 

 Holaster, abundantly represented in the Cretaceous, is very 

 nearly allied to Ananchytes, but has the anus supra-marginal. 

 In Cardiaster, again, which is also Cretaceous, there is the 

 additional character of the existence of a " fasciole," which 

 passes beneath the anus and is continued on the sides of 

 the test. As will be seen immediately, the presence of 

 " fascicles " that is to say, of circumscribed bands of micro- 

 scopic granules, occupying definite areas and positions on 

 the test is highly characteristic of the Spatangidce, towards 

 which Cardiaster thus makes an approach. 



Lastly, in the family of the Spatangidce or Brissidce 

 VOL. I. Q 



