BIVALVIA. 161 



Spec. Char. Testa sub-cordatd, transversd, incequilaterali, tenui, sub-l&mgatd ; antice 

 rotundatd, postice prodmtd et angulatd ; costis radiantibus obsoletis, striis concentricis 

 distantibus, maryine Integra. 



Shell somewhat heartshaped, transverse, inequilateral, thin, and nearly smooth ; 

 anterior side rounded, posterior produced and angular ; ribs or radiating lines obsolete, 

 concentric striae distant; ventral margin with a very gentle curve, and free from 

 crenulations. 



Length, 2f inches ; height, 2 \ inches. 

 Localities. Red Crag, Bawdsey, Button. 

 Mam. Crag, Chillesford. 



Recent, Greenland, North America, Nova Zembla. 



This species is abundant in the Red Crag at Bawdsey, but is very scarce in collections, 

 from the difficulty of obtaining a perfect specimen, the exterior being always more or 

 less eroded, and the shell becoming very thin and fragile ; the same may also be said 

 of those found in the sandy deposit of the Mammaliferous Crag Period at Chillesford. 

 This species is so well marked that there is no danger of its being confounded with 

 any other, it stands, as it were, upon the very confines of our generic limits, possessing 

 only the rudiments of those characters by which the majority of the shells in this 

 genus are so well distinguished, and which, indeed, are in general so prominently 

 displayed. The costae, if they may be so called, are, in the recent shell, but faintly 

 visible, and traces of them are left upon the thickened edges or undecomposed portions 

 of the fossil, most distinctly upon the anterior side ; the shell has much the aspect of a 

 mactra, and its surface is eroded in the same manner as in the generality of the shells 

 of that genus from the Crag. The posterior side of our shell has a squarish outline, 

 being obtusely angular at the extremity of the posterior lateral tooth, while the ventral 

 margin forms with the posterior side an angle not much less than 90, though in some 

 of the specimens from Chillesford that side is much more pointed. The arrangement 

 of the dental characters are those of a true Cardium, but they are like the costae, 

 evanescent, as if a corresponding prominence existed between the teeth and ribs : two 

 large, ovate, and deeply-impressed muscle marks are left in my specimens, seemingly 

 compensating in its powerful adductors for the deficiency of dental characters. 



Cardium Norvegicum and Cardium pygmaum are given in the 'List of Clyde Fossils,' 

 by Mr. Smith of Jordan Hill. 



Genus CHAM A,* Linn., 1758. 



GLOBUS (sp.) Klein, 1753. 

 STOLA. Browne, 1756. 

 JATRONUS. Adanson, 1757. 

 MACTIOPHYLLTJM. Gevers, 1766. 



* Etym. xhpri, Aristot, a kind of shell fish. 



