xviii SPATANGOIDEA 555 



the ventral one. One fasciole at least, but a peripetalous one 

 never present. The anterior ambulacrum grooved and different 

 from the rest. This family is represented in British waters by 

 two genera, Spatangus and Echinocardium. The former possesses 

 only a sub-anal fasciole, and has specially long curved spines on 

 the ventral plastron. It is represented by two species, S. pur- 

 pureas and & raschi, the latter being distinguished by a pointed 

 lower lip, It is a deep-water species, found in 100 fathoms and 

 over on the west coast. S. purpureas is fairly common in 



Fig. 250. Hemiaster philippi. x 2. (From Wyville Thomson.) 



rather shallow water. From observations made on specimens 

 kept in confinement it appears to burrow only so far as to leave 

 the petals uncovered ; hence there is no need of a peripetalous 

 fasciole. Echinocardium is devoid of the thicker spines on the 

 plastron, and has an internal fasciole and a perianal one as well 

 as the sub-anal. As already mentioned, it is a deep burrower. 

 It is represented by three species, E. cordatum, E. pennati- 

 fidum, and E. flavescens. The first, described as the type of the 

 Spatangoidea, has a deeply grooved anterior ambulacrum. In 

 the remaining two species this ambulacrum is not grooved. 

 E. flavescens has only six or seven pairs of pores in the posterior 



