BIVALVIA. 16] 
Spec. Char. Testa sub-cordatd, transversd, inequilaterali, tenui, sub-levigatd ; anticé 
rotundatd, postice productd et angulatd ; costis radiantibus obsoletis, striis concentricis 
distantibus, margine integro. 
Shell somewhat heartshaped, transverse, inequilateral, thin, and nearly smooth: 
anterior side rounded, posterior produced and angular; ribs or radiating lines obsolete, 
concentric striz distant; ventral margin with a very gentle curve, and free from 
crenulations. 
Length, 2% inches ; height, 2} inches. 
Localities. Red Crag, Bawdsey, Sutton. 
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 costz, 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 coste, 
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 pygmeum are given in the ‘ List of Clyde Fossils,’ 
by Mr. Smith of Jordan Hill. 
Genus Cuama,* Linn., 1758. 
Guosus (sp.) Klein, 1753. 
Srota. Browne, 1756. 
Jarronus. Adanson, 1757. 
Macropuyiium. Gevers, 1766. 
* Etym. yun, Aristot, a kind of shell fish. 
