CLASS I 



ECHINOIDEA 



273 



(a) Rhabdocidaris Desor (Figs. 381, 382). Test large and swollen. Poriferous areas wider 

 than in Cidaris, tlie two pores of a pair being distant and conjugated. Amb in general 

 straight. Tiibercles large, strongly crenulated, and more nunierous than in Cidaris. Spines 

 very stout, some cylindrieal or prismatic, often spiniferons. Chiefly Jura and Cretaeeous ; 

 less common in Tertiary and Recent. 





Fio. 379, 



Eucidaris tribuloides (Lam.). Receiit. Erilarged vievv of base of the 

 test and peristome, showing plated coveriug of the latter. 



Plf!. 380. 



Cidarid spines. A 

 C. alata Ag. ß, C 

 dorsata Braun. Trias 

 St. Cassian, Tyrol 

 C, C. florigemma Phill 

 Coral llag ; Wiltshire. 



Fig. 381. 



Rhaf}docldaris orUgnyana Desor. Upper 

 Jura; Kelheim- Winzer, Bavaria, ^.Frag- 

 ment of test, i/i. B, Amb plates enlarged. 



Fio. 382. 



Rhabdocidaris horrida 

 Morian. Middle Jura. 

 Spine, i/i. 



{b) Leiocidaris Desor. Like the preceding, but with uncrenulated tubercles. Spines 

 large, smooth, cylindrieal. Cretaeeous to Recent. 



(c) Stephanocidaris A. Ag. Test thin ; apical System larger than the peristome, the 

 plates feebly united. Recent. 



{d) Pliyllacanthus Brandt. Test large, swollen, and witheight to eleven lAmb plates 

 in a column. Amb broad, pores conjugated. Primary tubercles large, smooth. Recent. 



(e) Porocidaris Desor (Fig. 383). Amb broad and straight ; pores wide apart, conjugated. 

 Primary tubercles perforate and crenulate. Scrobicules transversely oval, with shallow 

 grooves radiating from the periphery toward the centre, with or without pores at the outer 

 extremity of the grooves. Tertiary and Recent. 



(/) Goniocidaris- Desor. Töst high, with nunierous coronal plates, and narrow Amb. 

 The median sutural regions of both areas are sunken, forming with the horizontal sutures 

 a zigzag, with pit-like depressions at the angles. Recent. 



VOL. I T 



