BIVALVIA. 55 



upon the posterior side, which deeply indent the shell, and are therefore always 

 conspicuous. The Cardium cognatum of Goldfuss is a very different shell, having a 

 posterior angle and oblique umbones. D'Orbigny (' Prodrome') has arranged our species 

 .with his genus Unicardiuni, in which he has been followed by Dr. Oppel (' Juraforinatiou') ; 

 but, having examined the muscular impressions and also those of the hinge, I can affirm 

 that Professor Phillips correctly discriminated the genus. 



Geological Positions and Localities. The specimens figured are from the Cornbrash 

 of Scarborough ; it occurs also in the Kelloway Rock of the same neighbourhood and in 

 Wiltshire. 



CARDIUM. WITCHELLI, Lye. Tab. XL, fig. 36. 



Testa parva ovato-trigona, convexa, umbonibas magnis prominentibus mediums, sub- 

 acutis, latere posterior e angulo obliquo et area postica planata, in medio sulco obliquo in- 

 structo ; dorso striis tenuissimis concentricis regularibi/s. 



Shell small, ovately trigonal, convex ; umbones mesial, prominent, and somewhat 

 pointed ; the anterior and lower margins are rounded ; the posterior margin is somewhat 

 angulated at its lower extremity ; the posterior side has a conspicuous, oblique angle, 

 separating a flattened, smooth, posterior area, which is traversed by a mesial, oblique furrow ; 

 the other portion of the surface has very fine, regular, concentric striations. The height 

 and length are equal ; the diameter through both the valves is somewhat less. 



The abruptness of the posterior angle, the flattened, smooth area, with its mesial 

 groove, appear to separate it from other allied Jurassic species. Possibly it may be a 

 dwarfed representative of a much larger form. 



Geological Position and Locality. The Great Oolite of Bussage, near Bisley Common ; 

 the process of crushing shelly portions of the white Oolite has yielded this little species 

 to Mr. Witchell. 



CYPIUCARDIA CAUDATA, Lye. Tab. XXXVI, figs. 8, 8 a. 



Testa transversa, subtriyona, obliqua, subdepressa, uiiiboiiibux mayn't*, elevatis, sub- 

 involutis, incurvis, latere postico oblique declivi, obtusangulo iiistrucfo ; lunula depressa ; 

 valvis striis lo/igitudinalibus tenuissimis, intequalibus, latere antico semcl striis radiantibus 

 tenuissimis decussatis. Nucleo striis obscuris radiaiitibus et concentricis. 



Shell transverse, subtrigonal, oblique, rather depressed ; umbones large, elevated, and 

 subinvolute ; the posterior side slopes obliquely downwards, and has a slightly defined, 

 obtuse angle ; the anterior side is moderately produced ; the lunule is strongly defined ; 



