CHAMA'CEA, or CHA'MID/E, a family of Conchiferous the third of the Acephalous or Headless Testacea, according to Cuvier, who places them between his Mytilacea (Mussel-like Testaceans), and his Cardiacea (Cockle-like Testaccans).
Under the Linmean genus Chama many heterogeneous forms were assembled ; and as G. Sowerby observes, " in his arrangement regular and equivalve shells are placed with such as are irregular and equi valve ; free shells with others that are attached to marine bodies ; and shells which have two distinct muscular impressions with others which have only one." Bruguiere first divided this genus, and Lamarck carried out the reformation. The latter makes the Chamicke to consist of the genera Diceras, Chama, and Etheria, placing Tridacna and Hippopus under his Tridaen6es, the first section of his second order Cenchiferes Mono myaires.
Cuvier made the Camacies consist of the genera Mama, Tridacna, Hippopus, Chama (Brug.), Diceras, and Isocardia.
The genus Chama has the following characters :—The valves are irregular, inclining for the most part to the orbicular shape, unequal, generally foliated or spilled externally, and adherent. The umbones arc distant, unequal, and curled or involute. Tho hinge consists of one thick oblique somewhat notched tooth, inserted into the groove of the opposite valve. There are two muscular impressions, and they are distant and lateral. The ligament is external, and divided into two portions at its posterior extremity. The animal (Psilopus of Poli) is less irregular than the shell, and cordiform, or heart-shaped; the two lobes of the mantle unite posteriorly, and in the commissure are two very short ciliated siphons, like those of Isocardia. Upon the abdominal mass a small cylindrical truncated bent foot rises. The mouth is small, and is furnished on each side with a pair of somewhat square and obliquely-truncated palpi. Deshayes states that all the indivi duals of the same species adhere by the valve of the same side, and that the umboncs curve in the same direction.
Broderip, in the first volume of the Transactions of the Zoological Society of London' (1834), where he describes several new species brought home by Mr. Cuming, says, "The shells are attached by their external surface to submarine bodies, such as corals, rocks, and shells, and have been observed at depths ranging from points near the sur face to 17 fathoms. These shells appear to be subject to every chango of shape, and often of colour, that the accidents of their position may bring upon them. Their shape is usually determined by the body to
which they are fixed; the development of the foliated lamina) which form their general characteristic is affected by their situation; and their colour most probably by their food and by their greater or less exposure to light. The Chama that has lived in deep and placid water will generally be found with its foliations in the highest state of luxuriancy; while those of the individual that has borne the buffeting of a comparatively shallow and turbulent sea will be poor and stunted. Lamarck has divided the species into two sections, namely, first, those the umbones of whose shells turn from left to right ; and, secondly, those whose umbones turn from right to left. M. Sander Rang, in his ' Manual,' has adopted thus division, to which I cannot subscribe, because it will not bear the test of examination. Two remarkable instances are now well known of regular bivalves of the same species, in which one specimen may be regarded as being the reverse of the other, namely, Lucina Childreni, and an inequivalvo Myti/as in the British Museum : and to come at once to the case before us, the same species of Comae is 'sometimes attached tie:, right, sometimes by the left valve ; or, in other words, In one indi vidual of the species the umbones will turn from left to right, while in another individual they will turn from right to left" The same author observes, that the distinction of the species appears to him to be difficult, the variety being infinite. The number of recent species given in Deshaveis edition of Lamarck (1835) is seventeen, Including Claim albida (Camostr6e of Do Itoiesy; Cleidoltrrus of Stutehbury). Broderip, in the paper above alluded to, describes eleven additional varieties not noticed by Desheyes, who has however some ations on the following species, C. Lazarus, C. grypholdcs, C. unkornis, C. asperella (the living analogue of C. echinulata in Lamarck's fossil list), and C. albida, well worthy the attention of the student. We elect as an example C. gryphottles (C. gigas, Linn.), which is famous for its enormous size. Individuals have been known to weigh above three hundred pounds. The byasus by which it adheres to rocks is so tough that in order to procure the shell it must be cut with an axe. The animal may be eaten, but its flesh is very tough. Some very large specimens are to be seen in the Gardens of the Zoological Society, Regent's Park. One of the valves is sometimes used as a font for baptism in country churches.