179 
C. aspera, and C. avicularia, are the only species noticed by 
Lamarck, as found fossil near Paris. 
CV. Isocardia. A heart-formed shell, with separated, involuted, 
and diverging beaks. The hinge formed by two flattened cardinal 
inserted teeth, and an isolated lateral tooth under the cartilage slope. 
This genus includes the Chama cor, Linn. I am not acquainted 
with any shells, decidedly of this genus, having been found in a fossil 
state ; casts, however, of shells very similar, are frequently found, 
and have been distinguished as bucardites. 
CVI. Cardium. An equivalved subcordated bivalve, the valves 
dentated or plicated on their internal margins. The hinge formed by 
middle and lateral teeth : the middle ones, two, oblique and approxi- 
mating, those in each valve, crucially receiving each other, by mutual 
insertion ; those of the side, remote and inserted. 
The shells of this genus are strongly characterized by the teeth of 
their hinge, and by the projection of their beaks ; the latter giving 
them a cordiform appearance. They are generally ornamented with 
longitudinal ridges, more or less prominent ; and frequently with 
strise, scales, or spines. The marks of attachment are two in number, 
and are but faint. 
Specimens of a cardium, resembling C. cEolicum , Linn, figured by 
Lister, Tab. 314, No. 150, are sometimes found among the interesting 
fossils of the whetstone pits, completely silicized ; and still retaining, 
very distinctly, the striae, disposed longitudinally, in the fore part, and 
transversely in the posterior part. 
Among the fossils of Plumstead is found a cardium, striated exactly 
in the same two directions as the preceding ; but the striae, especially 
the transverse ones, are much more minute and faint than those ot 
C. ceolicum ; agreeing in this respect, and indeed in all its characters, 
with C. discors, Lam. Plate XIII. Fig. 3, is a representation of the 
silicized shell of Devonshire, resembling C. ceolicum. 
In the Harwich or Essex cliff’, a shell somewhat like to C. muricatum, 
