116 Dr. T. Wright on Fossil Echinoderms 



and Desor consider them to be the same, and we agree with their 

 conclusion. 



Grateloup observes, in describing C. marginatus, " We ought 

 not to confound this species with that which I have described 

 (C Tarbellianus) , with which it has great affinities of form, figure, 

 and size. Its test has also a summit tres-renfie, convex, and 

 more elevated than in C. Tarbellianus; but its border is a little 

 less evase, and much less tranchant. The ambulacras are equally 

 shorter, more redresses, and of a more oval and acute form." 

 We have only to observe, that the characters here cited vary 

 in different individuals, and at most amount to that limit of 

 variation which we have alrcad}"^ observed is seen in all species 

 of Urchins, where a number of individuals of the same form are 

 assembled for comparison. 



Stratigraphical range. — This species is found in bed No. 2, 

 the yellow sand, associated with C. alius and the other forms 

 enumerated from that stratum; it has been found likewise in the 

 Miocene beds of Touraine, Landes, Naros, Bonifacio, Santa 

 Manza, Corsica ; and Dax. 



History. — First figured by Scilla, and afterwards by Leske. 

 Fine specimens are contained in the ^lus. Jermyn Street, 

 British Museum, Bristol Museum, and the Collection of the 

 Earl Ducie. The specimen in our cabinet is from Santa Manza, 

 and was sent us by M. Michelin. 



Clypeaster folium, Agassiz. 



Syn. Clypeaster folium, Agassiz andDesor's Cat. rais., Ann. Sc. Nat. 

 torn. vii. p. 131. 



Test subheptagonal, much depressed; borders thin and sharp 

 like Scutella; the petaloid ambulacra short, open, and ex- 

 panded below ; acutely lanceolate at the apex ; ambulacral 

 rosette small, and rising gently from the middle of the dor- 

 sum ; poriferous zones lie in angular depressions ; apical disc 

 small, with a central prominent madreporiform tubercle. 



Dimensions. — Antero-posterior diameter 1|^ inch, transverse 

 diameter 1^^ inch, height j-'yths of an inch. 



Description. — The general outline of this little Urchin, with 

 the structure of its ambulacral rosette, clearly prove it to be a 

 Clypeaster, whilst its depressed dorsal surface and thin border 

 show it to have affinities with Scutella. Its outline is subhep- 

 tagonal, with the anterior border slightly produced ; the petaloid 

 ambulacral areas are short and widely expanded below, tapering 

 and acutely lanceolate above ; their apices closely approach at 

 the vertex, and meet at the circumference of the madreporiform 



