ECHINOIDEA 



287 



membranous spaces between the plates. Tube-feet on the oral 

 side in 3 series. Primary spines of oral side ending in a large 

 hoof. Tridentate pedicellarise with leaf -shaped, not involute, 

 valves. Oj^hicephalous pedicellarise may occur. 



One species known from the British seas, and from the 

 Atlantic in general. 



1. Sperosoma Grimaldii Koehler. (Fig. 163.) 



Large tubercles of the oral side onty on the outer 4-5 plates, 

 rather irregularly disposed. The large, hoofed primary spines 



Fig. 



l63. — Sperosoma Grimaldii, oral side. Reduced. 

 (After Koehler, ''Monaco'', xii.) 



distinctly curved. Large tridentate pedicellariae up to 2 nmi. 

 length of head ; the valves are simply leaf-shaped, the outer part 

 of the valves filled up by a spiny mesh work. Oj)hicephalous 

 pedicellariae have not been observed in this species. Colour in 



