54 RABDOCIDARIS. 



Gems 2— RABDOCIDARIS,* Desor. 



This genus was formed by M. Desor to include all the large inflated Cidarites, which 

 are often as high as they are in transverse diameter ; their poriferous zones are likewise 

 wider than in the genus Cidaris, the pores forming a pair are placed wider apart, and con- 

 nected by a small horizontal sulcus. The ambulacra are straight, or very httle flexed. 

 The tubercles are large, and always strongly crenulated, and, in the fossil species at least, 

 proportionately more numerous than in the true Cidaris. The areolas are large, and often 

 elliptical ; the miliary zones are wide. The spines are large, and have a long and much 

 developed stem. 



The species at present referred to this genus are Oolitic and Neocomian. — Desor. 



A. Species from the Lias. 



Rabdocidaris Moraldina, Cotteau. PL V, fig. S. 



CiDAEis MOKALDiNA. Cotteau, Etudes sur les Echinides Fossiles, p. 33, pi. 1, figs. 



1—3. 

 Rabdocidakis mobaldina. Desor, Synopsis des Echinides Fossiles, p. 42. 



Test large, form unknown ; inter- ambulacral plates large ; areola oval, occupying a 

 considerable portion of the plate ; mammillary boss with a broad base, not much elevated, 

 summit deeply crenulated ; tubercle proportionately small, with a large perforation. 



The only specimen I have seen of this urchin is the one figured in PI. V. It was 

 collected by Mr. Moore from the Marlstone of Somerset. M. Cotteau, who first described 

 the species, founded it upon the imprint of a fragment. Judging from the size of the 

 single inter- ambulacral plate, it must have been a very large Cidarite ; the areolas are wide 

 and oval, and, from the space they occupy, they must have been confluent above and 

 below, and surrounded only by incomplete scrobicular circles ; the miliary zone was flat 

 and wide. This species has some affinities with Cidaris maxima, Miinster ; but it is dis- 

 tinguished from it by many marked characters: the inter-ambulacral plate is one half 

 larger ; the areola is not excavated out of the substance of the plate, as in Cidaris maxima, 

 but is level with the surface, and the mammillary boss forms a much larger eminence 

 thereon ; the summit is likewise broader and more deeply crenulated. 



" (oa/36oros, striated, caualiculated. 



