FROM THE GREY CHALK. 121 



beautiful and perfect specimens of Glyj)hocyphis radiafus, collected by the late M. Triger 

 from the Terrain Cretace of the department of the Sarthe, and from the study of these 

 M. Cotteau has been enabled to clear up doubts that had previously existed regarding the 

 structure of many of the species. This genus is nearly allied to Echinocyphis, which 

 presents a similar facies of lateral impressions on the ambulacral and inter-ambulacral 

 plates, but is distinguished from it by having the mammillons of the tubercles perforated, 

 whereas in EcMnocyphus they are imperforate. The apical disc is, likewise, solidly united 

 to the coronal plates in Gli/phocyphus, but slenderly so in EcMnocyphus. M. Agassiz 

 proposed the genus Hemidiadema for Urchins differing from the Diademas in one 

 character, that the ambulacral areas possessed only a single row of tubercles, and cited 

 as the type of this group Hemidiadema ?7((?os?«;?, Agass., from the Upper Greensand (Etage 

 Cenomanien) of Grandpre, Ardennes, a small species having the ambulacral tubercles 

 as large and even larger than the inter-ambulacrals ; this Urchin, it now appears, is a true 

 Glyphocyphis, with a single row of tubercles in its ambulacral areas — a character which 

 is only specific, and not generic, as far as we at present know. 



The genus Echinopsis, Agass., in which certain species of Glyphocyphus have been 

 placed, consists, according to its author, of " small, subconical, inflated Urciiins, with the 

 ambulacra nearly as large as the_ inter-ambulacra, and both ornamented with tubercles 

 perforated but not crenulated. Mouth small, with feeble incisions, differing from the 

 Diademas by the absence of crenulations on the tubercles." To this genus was referred 

 Echinopsis contexta, Ag., E. latii^ora, Ag., E. depressa, Ag., all of which are forms of 

 GIyp)hocypjhus radiafus and Glypticus KonincJcii, Forb. Echinopsis pusilla, Roem., and 

 Temnopleurus pulcheUiis, Coquand, must now likewise be added to the list. 



GLYPHOcypHUS RADiATUs, IIoBnin(/haus. PI. XXIX b, figs. 1, 2, a, b, c, d, e. 



t 



EcHiNDS EADIATUS, Homiiiffhaus in Gold/uss. Petref. Germanise, p. 124, tab. xl, 



fig. 13, 182ti. 



— — Agassiz. Prod., Mem. Soc. Nat. des Sc. de Neufchatel, 



t. i, p. 196, 1836. 



— — Desmonlins. Etudes sur lea Echinides, p. 292, No. 55, 



1S37. 

 EcpiNOPSis LATIPORA, Agassiz. Catal. Syst. Ectyp. foss., Mus. Neoc, p 9, 1840. 



— CONTEXTA, Agassiz. Ibid. 



— DEPRESSA, Agassiz. Ibid. 



Echinus badiatus, Vujardin. In Lamarck's Anim. sans Vert., 2e e'd., t. iii, 



p. 371, 1840. 

 Aebacia radiata, Roemer. Norddeutschen Kreidegebirges, p. 30, 1840. 



Echinopsis pusilla, Roemer. Ibid., pi. vi, fig. 10, 1840. 



Cyphosoma radiatum, Agassiz et Besor. Ann. Sc. Nat., 3e surie, t. vi, p. 352. 



Cat. rais. des Bcbinides, 1846. 



16 



