ACEPIIALA TESTACEA. 371> 



The Vknusid.e {Veims, Linn.) — 

 Comprise many sliells, whose common cliaractor is to have tlie teeth and laminae of the hinge collected 

 under the beaks in a sin,L,^Ie group. They are in general flatter and more elongated in a direction 

 parallel with the hinge than the Cardia. Their riljs, when there are any, are almost always transverse, 

 ^\liicli is tiie contrary of the rule in the Cardia. The ligament often leaves, behind the beaks, an 

 elliptical impression, to which the term vulva has been applied ; and in front of the beaks there is 

 ahnost always anotlier oval impression that has been called the anns.^ The animal has always two tubes, 

 capable of being more or less protruded beyond the shell, but they are sometimes united together 

 apparently in one ; and it has also a compressed foot wherewith to crawl. 



M. de Lamarck restricts the name Vemis to those which have three divergent teeth under the beaks. This cha- 

 racter is peculiarly distinct in the species with an oblong, slightly convex shell. [These have been separated by 

 Sowerby to form his genus Pullanira, to which he unites the Venerupis, Lam., believing that the latter do never 

 perforate rocks, but merely occupy the holes excavated by olher animals.] Some (^A'/ar^e, Sow./or Crasmna, 

 Lam.) have only two diverging hinge teeth, and resemble the Crassatella in their thickness and some other 

 characters. Among the he;irt-shaped species it is iniportant to notice those whose transverse ribs or stria: termi- 

 nate in crests or tuberosities on the posterior side ; and those which have longitudinal ribs and elevated crests. 

 They lead by degrees to the Ci/t/ierea, Lam., which has a fourth tooth upon the right valve, projecting under the 

 anus, and received in a corresponding fossa of the left valve. Thai'e are some species, as in Venus, of an elliptical 

 and elongated form, and others that are ventricose, among which is the famous species ( Venvs Dione, Linn,), that 

 originated the application of the name of the Goddess of Love to a sheH, and remarkable for the long pointed 

 spines that guard its posterior end. There are species too of an orbicular form with sbghtly curved beaks, in 

 which the impression of the retractor muscle of the tubes forms a large, almost rectilinear triangle. 



When the animals are better known, it is probable we may have to separate from Cytherea, — ]. The species of a 

 much compressed, lenticular shape, with beaks approximating to a point. There being no impression of the fold of 

 the cloak, we infer that the tubes are not extensile. 2. Those of a ventricose, orbicular form, which want the 

 impression just mentioned^ but have a very long imprint of the anterior muscle, as in Lucina. 3. The thick species 

 with radiated ribs and without the impression of the cloak, wliich connect the Venusidae with the Venericardia. 



There has been already separated from Venus the Capsa, Brug., which have on one side of the hinge two teeth, 

 and on the other one only, but biiid ; the shell has no anus, is considerably convex, oblong, and the impression 

 left by the retractor muscle of the foot is considerable ; and the Petricola, Lam., w^ith two or three very distinct 

 teeth, one of them forked, on each side of the hinge. Their form is more or less cordate; but, as they live in 

 cavities of stone, Lwhich they themselves perforate,] they become sometimes irregular. From the marks left on 

 the shell by the cloak, their tubes ought to be larger. 



Tlie Corbula:, Brug., similar in form to the triangular or heart-shaped Cythereae, have only a single strong tooth 

 in each valve, locking side by side. The Mgament is internal. The tubes ought to be short; and the valves are 

 rarely quite equal. The fossil species are much more numerous than those actually existing. Some live in the 

 interior of stones. [The Sphenia, Turton, separated from Corbula, and which has C. ros/rata as its type, has not 

 been aclopted by foreign Conchologists. Sowerby unites it to Mya.] 



The MactraiDjE {Mactra, Linn.) — 

 Are distinguished among the shells of this family because the ligament is internal, and is lodged on 

 both sides in a triangular fossa. They have all a compressed foot, fit to creep witli. 



In J/ac/rf7, Lam., the ligament is attended in the left valve, on both sides, with a lateral tooth, which locks 

 within two laminae of the opposite valve. Close to the ligament there is on both valves a tooth which is folded 

 into the shape of the letter V, the point being nearest the umbo. The tubes are short and united. We have some 

 species on our shores. t In the Lav/ffvons [Lisiera,'rxirton] the \a.teTn\ teeth are almost obliterated .- nothing is 

 noticeable but a small tooth near the internal ligament, and we may remark also a small exterior ligament : the 

 pnsterior side of the shell is the shortest. The valves gape a little. The tubes are separate and very long, as in 

 Tellina. One species {Mi/a /ilspanica, Chemn.) is native, living in the sand at the depth of several inches. 



THE FIFTH FAMILY OF THE ACEPIIALA TESTACEA— 

 The Inclusa, — 

 lias the cloak' open at the anterior end, or near the middle only, for the passage of the foot. The 

 opposite end is prolonged into a double tube, that can be pushed far beyond the shell. This is always 



* These terms are npt to mislcnt), unH jtre otherwise objcciioiiAlile. 

 The .Htu'lviit should r.-incmljer tluit the li^'-iiiiifin ia ;il\vays un the pos- 

 terior si'l<; of ilie beaks. 



t En/rinn, Lam., is allied to Mactra, but indifferently churncier- 

 ized. One portion of them may be Crassatellie. ^mphidesma, I.iim., 

 or Lieiil't of Montiijru, appi'ftr also to be aHiiied to Mactn ; but they 

 i,r<> too little known to assiijii to them a definite place. {EryrAna has 

 been since well defined \>y Sow-erby, who has characterized three 



Bpeeies. The same author has also ifiven a good definition of .-Imphi- 

 dcfMia. which is not synonymous with the Ligulii; but our limits 

 prevent us 1,'oiiig into detail. Ciimingia, Sowerby, bhould be plated 

 near lo Ainpliidesnm. It is remarkiible for the dissimilRrity of the 

 hirij:c of the two valves, one having a strong: lateral tooth on eacli .side 

 of the liijamciit. and the other beini; entirely desriiute of latec^il teeth. 

 The species are found in sand, in the fissures of rocka, and, bo far as ii 

 known, they are tropical.] 



