ARCA ; PECTUNCULUS. CHAMACE.E. 



409 



the foot, and by which the animals are affixed to submarine 



bodies. They reside near the 

 shore in rocky places. There 

 are some species in the 

 Mediterranean at the pre- 

 sent time ; and others abound 

 in the older fossiliferous 

 strata of Italy. In the 

 Pectunculus the hinge has 

 a similar elongated charac- 

 ter, but it is curved instead of being straight. 



FJG. 594. PECTUNCULVS. 



ORDER VII. CHAMACE^E. 



951 . In this Order are included the largest, and some of the 

 most inert, of all the testaceous Mollusca. Nearly all of them 

 are attached to rocks or other 

 solid bodies, during the great- 

 est part of their lives ; some 

 by the adhesion of the shell 

 itself, and others by a tendi- 

 nous prolongation of the foot, 

 which serves as a byssus. 

 The shell is generally more or 

 less irregular in form, in con- 

 sequence of these adhesions ; 

 its hinge is very analogous 

 to that of Unio, the left valve 

 being provided with a tooth, 

 and further back with a pro- 

 jecting plate, which are re- 

 ceived into corresponding prominences in the right valve. The 

 foot is generally very small, and the adductor muscle is double, 

 the anterior one, however, being sometimes rudimentary. The 



Chama is one of those attached by the shell itself to rocks y 

 corals, and even to masses of similar shells, in the manner of 



Oysters ; and the individuals are thus cemented so strongly to 



FIG. 595 CHAMA, with the shell removed, 



to show the arrangement of the mantle 

 and its orifice. The two lobes are adhe- 

 rent along their entire edges ; except at 

 the respiratory passages, r, and e, and to 

 give exit to the foot, /. 



