172 EOCENE MOLLUSCA. 
CHAMA. Pliny, Linne, &c. 
g; 
inequivalved, subequilateral, with a somewhat involute umbo. Hinge with two teeth in 
one valve, and one in the opposite inserted between them ; margins sometimes crenulated. 
Impressions by the adductors large and elongately oval; mantle-mark without a sinus ; 
connexus ligamental. 
Generic Character. Shell thick, strong, and adherent; irregular, rugose or foliated ; 
Animal with the mantle margins united and the edges fringed ; siphonal tubes short 
and large, not extending beyond the shell ; branchial one fringed ; foot short and bent. 
The exterior of the shells of this genus in the recent state is more or less ornamented 
with spines, or otherwise elegantly fringed, and they are generally much coloured. The 
spines are sharp, pointed, subtubulous and fimbriated, or sometimes broad and spatulate. 
In fossils the shells are covered with rugosities or spinous fimbrice, and are more or less 
radiated between them. Our Eocene species appear to have been attached by the left 
valve. Chama gryphoides of the Crag adhered by the right, and the recent species vary 
in this respect. 
This is a pretty well-marked genus, and its nearest relative is Diceras, from which it 
has probably descended. In that genus the valves are more involute, and where may be 
seen the external connector retreating in a groove up the spire as the shell increases and 
the umbo recedes. The same is visible, in a minor degree, in some specimens of our 
present genus, where the shell has adhered only by the umbo. The valves are generally 
unequal, and occasionally there is no mark of adherence on either valve; at others the 
animal has attached itself by the greater part of the surface of the lower valve. In some 
of the species the inner surface of the shell is finely punctured in a regular manner, 
from the peculiar composition of the shell. 
This genus is considered to indicate tropical or subtropical conditions, not extending 
northwards beyond the Mediterranean, and the animals live chiefly among coral-reefs. I 
am not aware of their having been found fossil lower than the older 'Tertiaries ; and, 
until lately, have they been known only in the middle series of that period. 
1. Cuama caucarata, Lamarck. Pl. XXV, fig. 1 a—e. 
Cuama cabcarata, Lam. Ann. du Mus., vol. xiv, pl. xxiii, figs. 4 a, d. 
_ _— Desh. Coq. Foss. des Env. de Par., p. 246, pl. xxxviil, figs. 5—7, 1825. 
Spec. Char. “C. Testa orbiculatd, turgidd, plicis transversis acutis distantibus ; 
superioribus spinis prelongis, canaliculatis, radiatim echinatis.”—Deshayes. 
Shell irregularly orbicular, thick, and strong, covered by prominent sharp, reflected, 
