NO. 3 CASSIDULOID ECHINOIDS — KIER 29 



longed, truncated at anal groove ; adorally, inflated anteriorly, sloping 

 posteriorly; adapically, peristome depressed, interambulacra slightly 

 inflated, ambulacra slightly depressed. 



Apical system. — Anterior, elongate, tetrabasal, with four genital 

 pores situated in distal corners of plates (text fig, 6) ; genital plates 

 2 and 3 separated from genitals 4 and i by oculars II and IV and 

 several complementary plates. In British Museum specimen B.M.E. 

 1505, seven complementary plates; number of such plates probably 

 quite variable. 



Ambulacra. — Petals slightly developed, open, extending over two- 

 thirds distance to margin, petals II, III, and IV straight, petals V 

 and I curved convexly, posteriorly; poriferous zones narrow, pores 

 oblique, inner pore of pair distal to outer; interporiferous zones wide, 

 increasing in width distally. 



Adoral intcranibulacra. — Two series of low, alternating plates ; in 

 interambulacram 5 plates larger than in other areas. 



Periproct. — Supramarginal, in contact with apical system, longi- 

 tudinal, in deep triangular groove increasing in width toward pos- 

 terior margin. 



Peristome. — Anterior, higher than wide, oval to subpentagonal. 



Pfoscclle. — Bourrelets slightly developed; phyllodes double pored, 

 with slight crowding of pore pairs (text fig. 7), no buccal pores. 



Tuber dilation. — Tubercles perforate, crenulate, slightly larger on 

 adoral surface than adapical. 



Occurrence. — Middle Jurassic (Bajocian-Bathonian) of England 

 and France. 



Location of type specimen. — Holotype in British Museum (Natural 

 History), No. B.M.E. 1579. 



Remarks. — H. caudatus has been considered generically or sub- 

 generically distinct from Hyboclypus because of its apical system, 

 which is elongate with complementary plates separating oculars II 

 and IV, and genital plates i and 4. In Hyboclypus the apical system 

 is also elongate and the complementary plates usually separate genital 

 plates I and 4, but not completely oculars II and IV, I do not believe 

 that this difference in apical system is of generic significance. The 

 arrangement and number of complementary plates is very variable 

 even within one species. In Hyboclypus gibberulus, according to 

 Cotteau's (1873, Pal. franc, Jur., pi. 93, figs. 7, 9) figures, in one 

 specimen there is only one complementary plate with both genital 

 plates I and 4 and oculars II and IV in contact, and in another speci- 

 men there are three complementary plates separating genitals i and 

 4 and partially oculars II and IV. 



