92 MOLLUSCA. 



serted into the extremities of the valves, whicli serve to close them. 

 In the 



Arca, Lam., 



Or the Arcae properly so called, the hinge is rectilinear, and the 

 shell most elongated in a direction parallel to it. The summits are 

 generally convex, and curve over the hinge, but are separated from 

 each other. The valves do not close perfectly in the centre, because 

 there is a horny plate or tendinous fillet, before the abdomen of the 

 animal * that serves for a foot, and by which it adheres to submerged 

 bodies. They are found in rocky bottoms near the shore, and are 

 usually covered with a hairy epidermis. They are not much esteemed 

 for the table. 



Some species are found in the Mediterranean f , and a great 

 many fossil, in strata anterior to chalk, particularly in Italy. 



Cert lin Arcae in which the teeth of the two ends of tlic hinge as- 

 sume a longitudinal direction, are distingiushed by Lamarck \mder 

 the name of CucuLL-iEA \. 



We ought also, it is probal.le, to separate the species with well 

 marked ribs, and completely closing and interlocking edges ; for we 

 must presume that their animal is not fixed, but rather resembles that 

 of a Pectunculus §. 



We have a still better warrant for removing the Arca tortuosa, 

 Chemn., VIII, liii, 524, 525, in its fantastic figure and unequally obli- 

 que valves II . 



Pectunculus, Lam. 



The hinge foraiing a curved line, and the shell lenticular; the valves 

 always close completely, and their summits are approximated. The 

 animal, Aximea, Poli, is furnished with a large compressed foot with 

 a double inferior margin which enables it to crawl. They live in 

 ooze. Some species are found on the coast ot France ^, 



NucuLA, Lam. 



The Nuculse are Arcae, in which the teeth are arranged on a broken 

 line. Their form is elongated, and narrowed near the posterior ex- 

 tremity. Their animal is unknown, but is probably not far removed 

 from those of the preceding shells **. 



This has long been the place assigned to the 



* The Daphne, Poli. 



t Arca No(C, Chemn., VII, liii, 529, 531 ■,—Arca barbata, Id., liv, 535, 537 ; — 

 A. ocata, lb., 538 ; — A. mageltanica, lb., 539; — A. reticulata, lb. 540; — A. Candi- 

 da, Id., Iv, 542, 544; — A. indica, lb., 543; — A. cancellata, Schroed., Intr., Ill, 

 ix, 2. 



X Arca cucuUata, Chemn., VII, liii, 526, 528 ; — Cucullaa crassatina, Lam., Ann. 

 du Mus,, VI, 338. 



§ Area antiruata, L. Chemn., VII, Iv, 548, 549 ; — A. senilis, Id., Ivi, 554, 556 ; 

 — A. granosa, lb., 557 ; — A. corbiculata, lb., 558, 559 ; — A. rhombo'idea, lb., 553 ; — 

 A. jamaiccnsis, List., 229, 64. 



II It forms the gennsTRisis, Oken. 



^ Arca pilosii, L., Chemn., VII, Ivii, 565, 56G ; — Arc. gli/cimeris, lb.. 564 ; — A. 

 deciissata, lb., 5G1 ; — .4. cequilalera. Id., 562 ; — A. undata, lb., 560 ; — A. mannoruta, 

 lb., 563; — A. pectunculus, Id., Iviii, 568, 569 ; — A. jwclinata, lb., 570, 571. 



** Arca pcllucida, Chemn., VII, liv, 541 ; — Arca roslrula, L., Id., Iv, 550, 551 ; 

 — Arc. pelki, lb., 546 ; — Arc. nucleus. Id., hiii, 574. 



