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XXXII. On the Genus Chama, Brug., with Descriptions of some Species apparently not 
hitherto characterized. By W. J. Broverip, Esq., Vice-President of the Geological 
and Zoological Societies, F.R.S., L.S., &c. 
Communicated December 23, 1834. 
THE genus Chama, modified as it was by Bruguiéres, includes only that section of the 
Linnean genus of the same name, the animal of which, under the title of Psilopus, has 
been described and figured by Poli. Lamarck and Cuvier have both adopted this 
arrangement of a group which is natural, gregarious, and whose geographical distribu- 
tion appears to be confined to the warmer seas, the Mediterranean being the locality of 
the lowest temperature where any of the species have been hitherto found. 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 surface to seven- 
teen fathoms. These shells appear to be subject to every change of shape, and often of 
colour, that the accidents of their position may bring upon them. Their shape is usu- 
ally determined by the body to which they are fixed; the development of the foliated 
lamine which form their general characteristic is affected by their situation ; and their 
colour most probably by the 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 folia- 
tions in the highest state of luxuriancy, while those of the individual which has borne 
the buffeting of a comparatively shallow and turbulent sea will be poor and stunted. 
Lamarck, with much reason, has placed the genus Chama properly so called between 
Diceras and Etheria ; but he has divided the species into two sections, viz. first, those 
the umbones of whose shells turn from left to right, and, secondly, those whose wmbones 
turn from right to left. M. Sander Rang, in his Manual, has adopted this division, to 
which I cannot subscribe, because it will not bear the test of examination. Two remark- 
able 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, viz. Lucina Childreni and 
an inequivalve Mytilus in the British Museum ; and, to come at once to the case before 
us, the same species of Chama is sometimes attached by the right, sometimes by the 
left valve ; or, in other words, in one individual of the species the wmbones will turn 
from left to right, while in another individual they will turn from right to left. 
The fossil species are numerous, and occur in the supracretaceous group, particularly 
in the Subapennine beds, and those of Bordeaux and Dax ; in the cretaceous group ; 
and also in that of the oolite. 
To me the distinction of the species of this genus appears to be difficult. Their 
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