FROM THE GREY CHALK. 



121 



beautiful and perfect specimens of Glyphocijpltus radiafus, collected by the late ^I. 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 EcUnocuphus, which 

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

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

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

 to the coronal plates in Glyphocyphus, but slenderly so in Echinocyphus. M. Agassiz 

 proposed the genus Ilemidiadema 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 niyosum, Agass., from the Upper Greensand (ICtage 

 Ccnomanien) of Grandprc, 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 

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

 is only specific, and not generic, as far as we at })resent know. 



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

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

 ambulacra nearly as large as the inter-ambulacra, and both ornamented w'ith 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. latipora, Ag., E. depressa, Ag., all of which are forms of 

 Glyp)hocyphus radiafus and Glypticus Koninckii, Forb. Echinopsis pusilla, Roeni., and 

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



Glyphocyphus radiatus, Haminyham. PI. XXIX b, figs. 1, 2, a, h, c, d, c. 



ECHIXUS RADIATUS, 



Echinopsis latipora, 



contexta, 



depressa, 



Echinus radiatus, 



Arbacia radiata, 

 Echinopsis pusilla, 

 Cypuosoma radiatum, 



Ilaninghaus 'm Goldjuss. Petref. Germaniae, p. 12-1, tab. xl, 

 fig. 13, 1826. 



Agassiz. Prod., Mem. Soc. Nat. des Sc. de Neufdiatel, 



t. i, p. 196, 1836. 

 Desmoulins. Eludes sur les Ecliinides, p. 292, No. 55, 



1837. 



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

 Agassiz. Ibid. 

 Agassiz. Ibid. 



Diijardin. In Lamarck's Anim. sans Vert., 2e ed., t. iii, 

 p. 371, 1810. 



Roemer. Norddeutsclien Kreidegcbirges, p. 30, 1840. 

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



Agassiz et Besor. Ann. Sc. Nat., 3e scrie, t. vi, p. 3r)2. 

 Cat. rais. des £cbinides, 1846. 



16 



