104 MOLLUSC A. 



only wanting, but where, as in the Lucinae, the impression of the 

 anterior muscle is very long * ; 



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 f. In the 



CAPSA, Brwj. 



Already separated from the former, there are two teeth on the 



hinge on one side, and a single, but bifid one, on the other ; the 



lunula is wanting, the shell convex, and the fold, indicative of the 

 retractor of the foot, considerable J. 



PETRICOLA, Lam. 



Also separated from the same genus ; the Petricolse. on each side, 

 have two or three very distinct teeth on the hinge, one of which is 

 forked. The shell is more or less cordiform, but as they inhabit 

 the interior of stones, it sometimes becomes every irregular. Judg- 

 ing from the marginal impressions of their mantle, their tubes must 

 be very large . 



CORBULA, Brug. 



Similar in form to the triangular Cytherese, or cordate ; but a single 

 stout tooth in the middle of each valve, corresponding to the side of 

 its antagonist. The lagiment is internal ; the tubes must be short, 

 and the valves but rarely equal ||. 



The fossil species are much more numerous than the living 

 ones^f. 



Some of them live in the interior of stones**. 



MACTRA, Lin. 



The Mactrse are distinguished from the other Testacea of this family 

 by their ligament being internal, and lodged throughout in a trian- 

 gular depression, as in the oyste'rs ; they all have a compressed foot 

 fitted for crawling. In the 



MACTRA, Lam., 



Or the Mactrse properly so called, the ligament is accompanied 

 to the left valve, before and behind, by a projecting plate which is 

 received between two others on the right one. Close to the ligament, 



* Fen. tigrina, Chemn., VII, 37, ?90 ; Fen. punctata, Ib. 397. 



t Fen. pectinata, Chemn., VII, 39, 419 the genus ARTHEMIS, Oken. 



J Yen. deflorata, Chemn., IV, ix, 79 82. 



Ven. lapicida, Chemn., X, 172, 1664, and the RUFELLARIA of M. Fleriau de 

 Bellevue ; Ven. perforans, Montag., Test. Brit. pi. iii, f. 6 ; Donax irus ? 

 Chemn., VII ; xxvi, 270. 



|| See Encyc. Method., Vers, pi. 230, f. 1, 4, 5, 6. 



*[ Corbula gallica ; G. complanata ; G. ombonella, Desh., Coq. Foss., des Env. 

 dc Paris, t. I, pi. 7, 8, 9. 



** Venus monstrosa, Chemn., VII, 42, 445446. 



