C H A ]M S T R E A . 



Plate I. 



Genus CHAMOSTREA, X»e Rois-Hij. 



Teda iHilde inaquioalvis, valcle inaquiluleralh, umboidbns iii- 

 volutis, latere postico acute trigono, untico piano, ad- 

 hrprenie ; vahd dexlrd perampUter trUjotw-convexd, 

 sinistra plouiuKculd, opercttloided. Cardo dente purvo 

 solido erecto in valvd sinistra in fossnlam valva dfxti'a 

 intranle, fossuldque alterd liyamentmi cum ossicnlo 

 conlinente, ligamento elonijato etiam ad marginem. 



Shell very inequivalve, very inequilateral, with the mnboes 

 involute, posterior side shai'ply triangular, anterior 

 fiat, adhering ; right valve very large, triangularly 

 convex, the left rather flat, lid-like. Hinge composed 

 of a small solid erect tooth in the left valve, entering 

 into a pit in the right valve, behind which there is 

 another pit containing elastic ligament, with an os- 

 sicle attached ; there is also a marginal ridge of liga- 

 ments. 



The animal of this curious Australian bivalve has been 

 described by Albany Hancock, but it is not at all clear 

 that the place assigned to it in the family of Anatinidce is 

 correct. The shell is of very solid growtli, flatly adhering 

 to foreign bodies by the right valve, which is deeply tri- 

 angular convex, while the left valve, which forms a lid to 

 it, is of very peculiar growth. The posterior portion of this 

 valve is developed, and corresponds with, the free posterior 

 portion of the right valve, and is of the same concentri- 

 cally striated growth, but the anterior portion of the left 

 valve, which is developed with the adhering portion of the 

 right valve, presents an abrupt change of growth, having a 

 crisped wrinkled surface, with the lines of increase ranging 

 obliquely. 



The hinge of Chamostrea is unique in structure. In the 

 left valve is a blunt erect tooth, fitting into a pit in the 

 right valve, beside which, in each valve, there is another 

 pit containing ligament with a shelly appendage or ossicle, 

 quite distinct from the shell, attached to it. The valves 

 open and shut with the aid of this moving ossicle, and in 



opening dried specimens of the shell it will be found ad- 

 hering to ligament either in the ligamentary pit of the 

 right or left valve as accident may ilirect. In the speci- 

 men represented in the accompanying Plate, at Fig. L /; and 

 1 c, the ossicle may be seen adhering to the ligament in the 

 left valve. At Fig 1 c? it is again given by itself. Along 

 the margin above the hinge is an auxiliary more elongated 

 portion of ligament. In Fig. 1 r it may be seen com- 

 mencing in a dark curve above the tooth-pit. 



Lamarck, on the authority of M. Lesehenault. gives 

 Java as the habitat of this shell, but this must be a mis- 

 take. The only satisfactorily authenticated habitats are 

 east coast of New Holland and New Hebrides. Fig. 1 c 

 shows the mode in which specimens adhere to one another. 



Species 1. (Fig. a, b, c, d, e, Mus. Cuming.) 



Chamostre.\ albida. Cham, testa irigono-globosd, solidd, 

 purpuri'O-rosed et fidvd, valvd dexlrd concentrice ru- 

 goso-striald, ralcre sinistra dimidio postico concentrice 

 rngoso-striato, altera oblique peculiariter crispato-cor- 

 rmjnto. 



The whitish Chajiostrea. Shell triangularly globose, 

 solid, purple-rose and fulvous, right valve concentri- 

 cally roughly striated, posterior half of the left valve 

 concentrically roughly striated, the other half ob- 

 liquely peculiarly crispately wrinkled. 



Chama albida, Lamarck, Anim. sans vert. vol. vi. p. 585. 

 C'hamostrea albida, De Roissy. 

 Cleidolharus Chamoides, Stutchbury. 

 Cleidotluerus albidits, Deshayes. 



Hab. Sydney, New Hebrides. 



The Australian specimens of this genus are strongly 

 hinged and rayed with pui-ple-rose. The specimens in 

 Mr. Cuming's collection from New Hebrides, one of which 

 is given at Fig. 1 a, are uniformly pale and livid. 



Februarv, 1863. 



