FROM THE CORNBRASH. 341 



specimens I have seen and collected have been, with only one exception, either entirely 

 denuded of the test, or else so eroded as to leave no structure visible. I send you the one 

 exception, which I found at Ellsworth about four years ago (fig. I a,c). It is narrower than the 

 usual form, which is quadrate — as broad as it is long. Mr. Brodie's specimen is con- 

 siderably larger, but, though having the test, it has been scraped and spoiled. Compared 

 with IV. clunicularis (of which I have seven beautiful specimens from the Cornbrash of 

 Rushden before me, four of these are depressed, and three high and conical), this nucle- 

 olite, among minor differences, presents the following main distinctions : 



Affinities and differences. — " 1st. Whereas in E. clunicularis there is always a narrow 

 depressed space (as long as the anal opening itself) between the apical disc and the vent ; 

 in E. GriesbacJiii there is no such space, but the anal aperture immediately adjoins the 

 apical disc (fig. \ a, c). 



" 2d. The apical disc is proportionally much larger than in E. clunicularis, in con- 

 sequence of which the apices of the ambulacra do not approach each other so nearly, and 

 the perforations in the disc are wider apart (fig. 1 b). 



" In this small urchin (fig. 1 a) the disc is fully as broad as in a fine specimen of E. 

 clunicularis — one inch and three tenths in antero-posterior diameter. 



" If several false species have been made out of E. clunicularis, that is no reason 

 why we should too readily unite different forms under that name. I think this i 

 a distinct species, and hope, therefore, to have avoided what might otherwise have been 

 said, ' Incidit in Scyllam cupiens vitare Charybdim.' I have no idea that this form 

 is rare in the Great Oolite, but it appears to have been overlooked." 



EcHiNOBRTSsus ORBICULARIS, FhilUps. PI. XXV, fig. 2 a, h, c, d, e,f,g. 



Clypeus orbicularis. Phillips, Geology of Yorkshire, tab. vii, fig. 3, 1829. 



— — Agassiz, Prodrome d'une Monogr. des Radiaires Mem. Soc. 



des Sc. Nat. de Neuchatel, t. i, p. 136, 1836. 



— — Dujardin, in Lamarck, Animaux sans vertfebres, 2d ed., 



t. iii, p. 348, 1840. 



— — Morris, Catalogue of British Fossils, p. 50, 1843. 

 NucLEOLiTES ORBICULARIS. Forbes, Memoirs of the Geological Survey, decade first, 



description of pi. vii, 1849. 



— — Wright, Annals and Magazine of Natural History, 2d series, 



vol. ix, p. 301, 1851. 



— — Forbes, in Morris's Catalogue of British Fossils, 2d ed., p. 84, 



1854. 

 Davoust, Note sur les Foss. Sp^ciaux, a la Sarthe, p. 25, 

 1856. 

 EcHiNOBRissus ORBICULARIS. Desor, Synopsis des Echinides Fossiles, p. 265, 1857. 



— — Cotteau and Triger, Echinides du departement de la Sarthe, 



— — pi. ix, figs. 5—8, p. 57, 1858. 



