88 



PSEUDODIADEMA 



DlABEMA KOTULARE, 



— MACROSTOMA, 



— ROTULAKE, 



Dtadeua DUBIUM, 



— ROTULARE, 



PsEUDODIADEMA 



MACROSTOMA, 



ROTfLARE, 



PIETETI, 



TRISERIALE, 



- ROTULARE, 



PERIQUETI, 



MACROSTOMA, 



- TRISERIALE, 



D'Orbigiiy. Prod. dePalcont. Stmt., t. ii, p. 89 ; Et. 17, No. 489, 



1850. 

 B'Orhigny. Ibid., No. 491, 18.")0. 

 Cotfeau. Cat. Ecli. Neocom., Bull. Soc. de I'Yonne, t. v, p. 285, 



1851. 

 Sharpe. Sands and Gravels of Farringdon, Quart. Journ. Geol. 



Soc, vol. X, p. 194, 1853. 

 Forbes. In Morris's Catalogue of British Fossils, 2nd ed., p. 7G. 



1854. 

 Cotteau. Paleontologie Francaise, Ter. Cretacc, vol. vii, p. 422, 



pi. 1097, figs. 11-13; pi. 1 098 and 1099. 

 Desor. Synopsis des Echinides fossiles, p. 69, 1856. 

 Besor. Ibid., p. 68. 

 Cotteau. Etudes surlesEclnnides de I'Yonne, t. ii, p. 24, pi. xlix, 



figs. 1—5, 1857. 

 Cotteau. Ibid., p. 31, pi. 1, figs. 7 — 10, 1857. 

 Desor. Synop. des Echin. foss., p. 445 (Suppl.). 1858. 

 BujarJin et Hupc. Hist. Nat. des Zoophytes, Ephinoderm., p. 



42S, 1862. 

 Dujardin et Hupc. Ibid. 

 Dujardin et Hupc. Ibid. 

 Dujardin et TIupv. Ibid. 



Test small, circular, sliglitly pentagonal, moderately convex above, and flat below ; 

 poriferous zones narrow, straight ; pores in single file ; ambulacral areas large, two 

 rows of close-set marginal tubercles ; inter-ambulacral areas, four rows of tubercles at 

 the ambitus, the outer rows disappearing on the upper surface; miliary zone wide, 

 depressed near the disc, and covered with an abundance of well-formed granules. Mouth- 

 opening large, decagonal ; peristome deeply notched ; lobes unequal. 



Dimensions. — Height four tenths of an inch ; transverse diameter, one inch. 



Description. — This is a very rare Urchin from the remarkable deposit of fossiliferous 

 sands and gravels near Farringdon in Berkshire, about the age of which so many different 

 opinions have been given ; perhaps the Echinidge found therein may assist to determine the 

 problem whether these beds belong to the Lower Greensand, or to a " more modern member 

 of the Cretaceous Series than the Chalk," as maintained by the late Mr. Daniel Sharpe, 

 E.G.S.^ The Diadema now before us is a well-known and characteristic species, of the 

 middle stage of the Neocomian formation, containing Echinosjiatagus cordiformis ; and the 

 extensive table of synonyms prefixed to this article shows hoAv widely it is distributed in 

 beds of the same age on the continent of Europe. 



The test is of medium size, circular or slightly pentagonal, moderately convex on the 

 npper surface, and nearly fiat beneath. 



1 " On the Age of the Fossiliferous Sands and Gravels of Farringdon and its Neighbourhood," ' Quart. 

 Journ. of the Geological Society,' vol. x, p. 176. 1853. 



