BIVALVIA. 53 



general aspect resembles T, duplicata, Sow., but it has no bifurcating costae near to the 

 lower border, and is also destitute of concentric costae near to the apex. The sole specimen 

 at our disposal is imperfect at the posterior extremity ; it has twenty costae, and would 

 require about four others to complete its surface. Possibly Trigonia Cybele, D'Orb., 

 from the Great Oolite of Luc, may not differ from this species, but the seven words allotted 

 to it in the ' Prodrome' of that author are insufficient to characterise it. 



The figure is nearly that of an equilateral triangle, each of the sides having a length 

 of about an inch. 



Geological Position and Locality. In rubbly, hard, ferruginous Oolite (Great Oolite) 

 from the Box Tunnel ; communicated by W. Walton, Esq. 



CARDIUM LINGCLATUM, Lye. Tab. XXXIII, figs. 2, 2 a; Tab. XXXV, figs. 11, 11 a. 



Testa ovato-oblonga, mediocriler convexa, umbonibus prominentibus, mediants, subacutis, 

 valvis maryinibus ellipticis curvatis, rugis concentricis irregular ibus, striisque tenuibus, 

 delicate impressis ; postice striis obliquis regularibus decussatis. 



Shell ovately oblong, moderately convex ; umbones prominent, mesial, and subacute ; 

 the anterior, posterior, and inferior margins of the valves are elliptically curved ; the 

 surface has numerous irregular, concentric rugae, and delicate, regular striations ; the 

 posterior side has some regular, oblique striations, which decussate those which are con- 

 centric. The height and the transverse diameter are equal. 



Allied to Cardium coynatum, Phil, but the latter has much greater convexity, it has 

 larger and less pointed umbones, its surface is also destitute of the concentric rugae and 

 striations. 



Geological Position and Locality. The Great Oolite of Kirklington, Oxon., collected 

 by J. F. Whiteaves, Esq. 



CARDIUM INCERTUM, Phil. Tab. XXXV, figs. 14, 14 a. 



CARDTOM INCERTUM, Phil. Geol. York., i, pi. 11, fig. 5. 

 UNICARDIUM INCERTOM, D'Orb. Prodrome, i, p. 279, No. 323. 

 CARDIUM INCERTUM, Morris. Catal., 1854, p. 192. 



Testa suborbiculari convexa, Icevi, umbonibus submedianis elevatis subacutis incurvis, 

 margine antico concavo, lunula subnuHa ; latere postico planato angulo obliquoformante, 

 maryine postico subrecto in/erne angulato ; lateribus plicis concentricis paucis, irmju/uribus 



et tenuibus. 



Shell suborbicular, moderately convex, smooth ; umbones mesial or slightly antero-mesial, 

 elevated, acute, and incurved ; anterior border concave and rounded ; lunule scarcely 



