FRO:\I THE INFERIOR OOLITE. .331 



Clypeus rimosus, Agassiz. 



Clypeus kimosus. Agassiz and Desor, Catalogue raisonue des Echinides des Sciences 

 Naturalles, S^serie, tome vii, p. 156. 

 — — Desor, Synopsis Echinides Fossiles, p. 277. 



This urchin was entered in the catalogue raisonne as, " Espece plate, discoide, a 

 arabulacres costules, Terr., Jiirass. du Gloucestershire, Deluc ;" in the ' Synopsis des 

 Echinides Eossiles,' M. Desor gave the following detailed diagnosis of it : " Species dis- 

 coidal, slightly convex, subrostrated posteriorly ; ambulacral summit central ; aual valley 

 very narrow, extending to the apical disc ; ambulacral petals convex and prominent, with 

 very large poriferous zones, which equal in width the inter-poriferous spaces ; base 

 undulated, peristome excentrally forwards ; the pores disposed in double ranks in the 

 phyllodes ; oral lobes small and not approximated." M. Desor, in a note, adds, " by its 

 general form, as well as by its costulated petals, this species approaches much to C. 

 Michelini, A-Vr., but the poriferous zones, instead of being distinguished by their 

 narrowness, are remarkable for their breadth. Should it happen to be demonstrated by a 

 series of examples that this character is not constant, it would be possible to unite these 

 two species." 



After a careful examination of all our Oolitic Clypei, with the view to identify M. 

 Deluc's specimen, which was said to have been collected from the Inferior Oolite of 

 Gloucestershire, I have been unsuccessful. 



Long before the publication of M. Desor's Synopsis, it occurred to me that C. rimosus 

 might be a variety of C. Michelini, one character, however, pointed out in the diagnosis, 

 " poriferous zones very large, equalKng the inter-poriferous space," is sufficient to prove 

 that this is not the case, seeing that C. Michelini is as remarkable for the narrowness of the 

 petaloid portion of the poriferous zones, as C. rimosus is for their breadth, and this 

 character is constant in the large series of specimens I have examined. The breadth of 

 the poriferous zones establishes an affinity with C. Miilleri, but in that species the test is 

 oval, the ambulacra are on the same plane with the inter-ambulacra and not costulated as 

 in C. rimosus. It is probable that this urchin may prove to be a depressed variety of 

 C. Plotii. 



