54 SUPPLEMENT TO GREAT OOLITE MOLLUSCA. 



defined ; posterior side forming a flattened area, well separated from the other portion of 

 the surface by a clearly defined, oblique, and acute angle ; the posterior border, at first 

 curved, slopes suddenly downwards, nearly in a straight direction, forming an angle at its 

 junction with the lower border ; the surface has a few faintly marked, irregular, concentric- 

 plications. 



Dimensions. Length, 13 lines ; height, 1 1 lines ; diameter through both of the valves, 

 8 lines. The hinge has not been examined. 



Geological Positions and Localities. The fine specimen figured was collected by J. F. 

 Whiteaves, Esq., in the Great Oolite of Kirklington, Oxon. It occurs rarely in the Inferior 

 Oolite of Blue Wick ; it was also collected in the roe stone of the Inferior Oolite at Leek- 

 hampton Hill by the Rev. P. B. Brodie. 



CARDIUM COGNATUM, Phil. Tab. XXXVI, figs. 3, 3 a. 



CARDIUM COGNATUM, Phil. Geol. York., i, t. 9, fig. 1-4. 



COGNATUM, Mow*. Catal., 1854, p. 192. 

 UNICARDIUM COGNATUM, D'Orb. Prodr., Et. x, No. 324. 

 Oppel. Juraformation, p. 410. 

 CARDIUM Leckenby. Journ. Geol. Soc., xv, pi. 3, fig. 8. 



Testa ovato-orbiculari, convexa, mnbonibus magnis, medianis, subrectis, margine 

 antico et postico, elliptico curvato, lunula nulla ; valvis striis concentricis, crebris, instructis; 

 postice striis radiantibus obliquis decussatis. 



Shell ovately orbicular, convex ; umbones large, prominent, mesial, straight, or directed 

 slightly forwards ; the anterior and posterior margins of the valves are curved elliptically ; 

 there is no lunule ; the whole surface has very densely arranged, delicate, concentric 

 striations; the posterior side is not compressed, but has some oblique, faintly marked 

 striations, which produce a roughened surface where they decussate the concentric 

 striations. 



The specific characters are not strongly defined, and reside more in the general figure 

 than in the ornamentation of the surface ; the Cornbrash specimens have a thin, shining 

 test, and the striations can scarcely be distinguished without the aid of a magnifier ; the 

 posterior side is scarcely so much produced as the other, and the greatest convexity of 

 the valves is placed a little posterior to the mesial line; the Kelloway Rock examples 

 are smaller. 



Cardium cognatum is nearly allied to an inferior Oolite species, casts of which are 

 very common in the Cotteswold Hills ; the latter fossils are more ovate, the muscular 

 scars more strongly impressed ; the test is much more thick ; the striations, both 

 concentric and oblique, are more strongly defined, especially the oblique striations 



