SPATANGOIDEA 5 5 5 



the ventral one. One faseiole 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 EcMnocardium. The former possesses 

 only a sub-anal faseiole, and has specially long curved Spines on 

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

 pureus and S. 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. purpureus is fairly common in 



Fia.250.—HemiasterphUippi. x2. (From Wyville Thomson.) 



rather shallow water. From observations made on specimens 

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

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

 faseiole. Ecliinocardium is devoid of the thicker spines on the 

 plastron, and has an internal faseiole 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. fiavescens. 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. fiavescens has only six or seven pairs of pores in the posterior 



