ORDER TESTACEA. i 
2. Those of a convexly orbicular form, in which the fold is 
not only wanting, but where, as in the lucine, the impression 
of the anterior muscle is very long. (Venus tigerina, Chem.) 
3. The thick species with radiated ribs, in which the fold is 
also wanting, and which connect the genus Venus with that 
of the Venericardia. (Venus pectinata.) In the 
Capsa, Brug., 
Already separated from the former, there are two teeth on the 
hinge at one side, one only, but bifid, at the other; the lunula 
is wanting, the shell convex, and the fold indicative of the 
retractor of the foot, considerable. (Venus deflorata.) 
PETRICOLA, Lam., 
Also separated from the same genus: the petricolz on each 
side have two or three very distinct teeth on the hinge, one of 
which is forked; the shell is more or less heart-shaped, but as 
they inhabit the interior of stones, it sometimes becomes very 
irregular. Judging from the marginal impressions of the 
mantle, their tubes must be very large. (Venus lapicida, 
Chemn., &c.) 
CoRBULA, Brug. 
Similar in form to the triangular cytherez or cordate: but a 
single stout tooth in the middle of each valve, corresponding 
to the side of its antagonist ; the ligament is internal, the tubes 
must be short, and the valves but rarely equal. 
The fossil species are much more numerous than the living 
ones. (Corbula gallica, &c.) 
Some of them live in the interior of stones. (Venws mon- 
strosa, Chemn.) 
MactTRA, Lin. 
The mactre are distinguished from the other testacea of 
