172 EOCENE MOLLUSCA. 



CHAMA. Pliny, Limie, &c. 



Generic Character. Shell thick, strong, and adherent ; irregular, rugose or foliated ; 

 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. 



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 fimbriae, 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. 



\. Chama calcarata, Lamarck. PI. XXV, fig. 1 a — c. 



Chama calcakata. Lam. Ann. du Mus., vol. xiv, pi. xxiii, figs. 4 «, h. 



— — Besh. Coq. Foss. desEnv. de Par.,p. 246, pi. xxxviii, figs. 5 — 7,1825. 



Bj)ec. Char. " C. Testa orbiculatd, turgidd, plicis transversis acutis distantibus ; 

 superioribus spinis pralongis, canaliculatis , radiatim echinatis." — Deshayes. 



Shell irregularly orbicular, thick, and strong, covered by prominent sharp, reflected, 



