XVIII 



ENDOCYCLICA 



535 



off the western coast of Ireland and Scotland. It also occurs in 

 the Mediterranean, and has been carefully examined and described 

 when living by Prouho.^ From his description it appears that 

 locomotion is effected almost entirely by spines, and that the 

 tube-feet of the lower parts of the radii have each in the centre 

 of the disc a pointed sense-organ like those in the centre of the 

 first tube-feet of the just metamorphosed Echinus, whilst those 

 of the aboral surface have no suckers. 



Fig. 237. — Goniocidaris canaliculata. x 2. (From Wyville Thomson. ) 



Fam. 2. Echinothuriidae. — Endocyclica with a large peri- 

 stome and comparatively small periproct. The peristome has a 

 regular series of ambulacral plates bearing pores for tube-feet, 

 but no interambulacral plates. No specially modified buccal 

 tube-feet, but external gills are present, and internal gills 

 (Stewart's organs) also occur. The periproct is covered with 

 numerous small plates. All the plates of the corona are 

 separated by thin slips of flexible body wall. Numerous com- 

 paratively short primary spines on both ambulacral and inter- 

 ambulacral plates ; these spines are covered on the tips with a 

 layer of hard dense material. 



' Loc. cit. 



