CHAMA. 
Puate I. 
Genus Chama, Linneeus. 
Testa orbicularis, vel oblongo-ovata, irreqularis, inequival- 
vis, spinis squamis lamellisve profuse ornatd ; valva 
inferiore plus minuse profundé concavi, superiore pla- 
niore ; umbonibus inequalibus, distantibus, nunc dex- 
trorsum, nune sinistrorsum, in eadem specie involutis. 
Cardo dente unico, crasso, obliquo, subcrenato, inserto. 
Tnpressiones musculares due, laterales,subample. Liga- 
mentum externum, post umbones divaricatum. 
Shell orbicular, ovate or oblong-ovate, irregular, inequi- 
valve, profusely ornamented with spines, scales or 
lamelle; lower valve more or less deeply convex, 
upper valve flatter; umbones unequal, distant, invo- 
luted sometimes to the right, sometimes to the left 
in the same species. Hinge composed of a single 
thick oblique slightly crenated tooth, inserted in a 
correspondingly grooved pit in the opposite valve. 
Muscular impressions two, lateral, rather large. Lig- 
ament external, divaricate behind the umbones. 
There is no genus of acephalous mollusks, excepting 
perhaps the Oysters, whose shells are liable to so much 
variation in form and general aspect, according to circum- 
stances of habitation, as the Chame ; it is easy to conceive 
that the growth of such parasitical genera would be more 
or less affected by irregularities in their place of attach- 
ment, but the Chame are more than usually distorted on 
account of their inhabiting the most confined situations, 
such as the crevices of rocks, and fissures of madrepore, 
without the power, possessed by most terebrating mol- 
lusks, of abrading or absorbing the obstacles to their natu- 
ral advancement. The species are thus extremely difficult 
to define, and the difficulty much increases in consequence 
of the dissimilitude frequently presented in the same species 
under different circumstances of habitation ; as for example 
between a specimen that has grown without interruption 
on a smooth surface, and one that has been formed within 
a very limited area, subject to external pressure; also 
between one that has had the opportunity of developing its 
luxuriant foliations undisturbed in calm and placid water, 
surrounded by food most favourable for the secretion of 
embellishment and colour, unaffected by exposure to light, 
and one which having to contend with the buffeting of the 
waves has become rude and stunted. Some species attach 
in groups one upon the other, others adhere by the ante- 
rior side only of the under valve, assuming the form of, as 
it were, a triangular cornucopia. 
Notwithstanding these irregularities, the Chame, di- 
vested of the Tridacne, Hippopi, Isocardie, Cardite ®&e., 
included with them by Linnus, constitute a very natural 
and extended genus, distinguished by colouring and ex- 
ternal sculpture in the form of spines, scales, lamelle &c., 
scarcely inferior in beauty and variety to the Spondyli. 
Lamarck divided the genus Chama into two sections, 
one including species with the umbones turned to the right, 
the other with them turned to the left; in which arrange- 
ment he has been followed by M. Rang; but it is clear 
from an examination of the magnificent series of from fifty 
to sixty species collected by Mr. Cuming, and which fur- 
nishes the whole of the material required for the present 
investigation, that this is merely a variation of growth com- 
mon to the same species. Mr. Broderip has already 
noticed this fact in a memoir in the ‘Transactions of the 
Zoological Society’ vol. 1. p. 301. containing descriptions 
of a few of the most striking species of Mr. Cuming’s col- 
lection, and it only remains to refer the reader for an illus- 
tration of it to Plate III. of the present monograph, in 
which I have represented two individuals of the same 
species, one at f. 10a, with the umbones turning from 
left to right, the other f. 10 4, with these processes di- 
rected from right to left. This is undoubtedly a feature 
of very rare occurrence, but it is nevertheless a condition 
of growth precisely analogous to what has been observed 
in the Lucina Childreni, and is so common, amongst uni- 
valves, in the Bulimus citrinus and others; the great 
majority of species are still, however, so far as we know at 
present, some constantly dextral, others constantly sinis- 
tral, as in the genus 47ca. 
Like all species of vivid colouring and luxuriant growth, 
the Chame are chiefly inhabitants of the tropical seas: they 
abound principally on the coast of Central America, Peru, 
Mexico, Honduras and the West Indies, some are found 
among the Pacific Islands, others in Australia, China, and 
the Philippine Islands, and their northern limit is in the 
Mediterranean. 
Species 1. (Fig. @ and 4, Mus. Cuming.) 
CHama FRONDOSA. Cham. testd ovatd, vel subquadrato- 
ovata, anticé plus minusve lobatd, creberrime irregula- 
riter lamellosd, lamellis subtiliter radiatim plicatis, 
sinuosis, in seriebus duabus, und posticd, und mediand, 
ab umbone radiantibus, multo majoribus, pulcherrimé 
Srondosis ; intus valvarum marginibus minutissime cre- 
nulatis et corrugato-striatis ; croced, purpureo hic illic 
tinctd, intus ceruleo-albidd, prope margines purpured. 
THE FRONDOSE CHaMA. Shell ovate, or somewhat squarely 
ovate, more or less lobed, very closely irregularly 
lamellose, lamellz finely radiately plaited, sinuous, 
in two rows, one posterior, the other medial, radiating 
from the umbone, the lamelle are much larger and 
very beautifully frondose ; interiorly the edges of the 
valves are very minutely crenulated and wrinkled 
with striae; bright saffron yellow, stained here and 
there with purple, interior blueish white, stained with 
rich crimson purple towards the edge. 
December, 1846. 
