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Show 418 MOLLUSCA. .m g from t h e marg1· na• l impressions of their mantle, th. eir tubes must be very large( 1 ). CousuLA, Brug. s• . · r • t t11e triangular Cytherece, or cordate; but a single. 1mllat· m 101m o . . stout toot l1 m· tl1 e m'tddle of each valve, correspondmg to the stde of its antagom· st. 'fl1 e ligament is internal; the tubes must be short, and the valves but rarely equal(2). The fossil species are much more numerous than the living ones(3). . . Some of them live ln the mtenor of stones( 4). MACTRA, Lin. The M actrce are d1. s t'tnguishecl from the other T'estacea of t.h is fam. ily by their ligament being internal, and lodged throughout m a tmn· gular d epress1· 0n, as in the oysters·' they all have a compressed foot fitted for crawling. In the MAoTRA, Lam., Or the Mactrce properly so called, the ligament is accomp_anie.d to the left valve, before and behind, by a projecting plate .wluch 1s received between two others on the right one. Close to the hgam~nt, near the lunule, is a little plate en chevron. The tubes are umted and short( 5). Some of them are found on the coast of France. . In the LAVIGNONS, the lateral plates are almost effaced, but a 51~· gle small tooth is observable near the internal ligament; there ~s also a second and internal ligament. The posterior side of the shellts '1 · de (1) Ven. la'Picida, Chemn., X, 172, 1664, and the RuPELLA.RIA of M.I• eri~U · 1 ··· f. 6· Dona:c tru8.2 Bellevue;-Ven. perforans, Montag., Test. Br1t. p · m, · ,- Chemn., VI; xxvi, 270. (2) See Encyc. Method., Vers, pl. 230, f. 1, 4, 5, 6. d E (3) Corbula gallica,·-G. complanata,·-G. ombonella, Desh., Coq. Foss., es nv. de Paris, t . I, pl. 7, 8, 9. (4) Venusmonstrosa, Chemn., VII, 42,445-446. fG . ' T.. • th 1\{A.CTRA 0 me (5) After abstracting the Lamgnones and .uutrartro, e genus . . . h d lin may remain as it is; the species, however, are far from b e·m g we 11 d 1s tmgms e · Add, Mya australis, Chemn., VI, iii, 19, 20. b dl barac· The EnYCINjE, Lam., are neighbours of the Mactrre, and are but a _yc f terized. See Ann. du Mus., IX, xxxi, and Deshayes, Coq. F oss., I ' VI"' part o them perhaps belong to the Crassatella:. The AMPHTDF.SMjE, L am . , or LxGULJIt! , Mont' ag., appe' ar to approach the Mactra:, but they are too 1. mpe rfectly known o have any distinctive chal'acter assigned to them. ACEPHALA TEST ACEA. 419 the shortest; the valves are somewhat open, and the tubes are separate and very long, as in the Tellince. There is one found on our coast, Mya hispanicd, Chemn. VI, iii, 21, which lives in the ooze at the depth of several inches)). FAMILY V. INCLUSA(2). The mantle open at the anterior extremity, or near the middle only, for the passage of the foot, and extended from the other end into a double tube, which projects from the shell, whose extremities are always gaping. Nearly all of them live buried in sand, stones, ooze or wood. Those of the genus MYA, Lin. Have but two valves to their oblong shell, the hinge of which varies. The double tube forms a fleshy cylinder, and the foot is compressed. The different forms of the hinge have furnished Messrs Daudin, Lamarck, &c., with the following subdivisions(3), in the fi1·st three of which the ligament is internal. LuTRARIA, Lam., The Lutrari~, like the Mactt·ce, have a ligament inset·ted into a large triangular cavity of each valve, and before that cavity a small tooth en chevron; but the lateral plates are wanting; the gap of the valves is very wide, particularly at the posterior extremity, through which passes the thick, double, fleshy, respiratory and anal tube, a disposition which attaches them to this family. The foot, which issues at the opposite end, is small and compressed. (I) Improperly called by Gmelin Mactra piperata. Add Mact1·a papyracea, Chemn., VI, xxiii, 231;-Mact. complanata, Id., xxiv, 238;-Mya nicobarica, Id., iii, 17, 18. (2) M. de Blain ville makes two families of this one, his P rLORIDEA. and ADEsl!u.cu. The last includes Plwlas, Teredo, and Fistulana.- the first, all the others, ~d even .O.spergillum. There are numerous genera established in this family too shghtly characterized to permit us to adopt them. (~) N.B. Half the Mya: of Gmclin neither belong to this genus, nor even to this family, but to Vulsella, Unio, M:actra., &c. . |
