Case 196.
The genus Chama consists of tropical species, which are found fixed to corals, rocks, etc. Nevertheless, they have a small bent foot, but what purpose it serves is difficult to conceive.
In this place attention should be called to the Hippuritidæ and Radiolitidæ, very remarkable extinct families of bivalved molluscs which occur abundantly in the cretaceous strata of southern and eastern Europe, Egypt, etc. They are remarkable for the solidity of the shells, the relatively small space occupied by the animal, and the complicated character of the hinge and processes bearing the adductor muscles. They are usually classed near to the Chamidæ, but their true position as regards living Mollusca is very problematical. A fine series of these shells is exhibited in Gallery VIII., wall-case 5, in the Geological Department.
Cases 198–199.
The Myidæ, popularly known as “Gapers,” on account of their valves being open at one or both ends, have the mantle united all round, except where the small foot is protruded. The siphons are very long, united almost to the ends, and covered with a coarse wrinkled outer skin. They bury themselves in mud and sand at low-water mark or in shallow water. The species are few in number, and chiefly from the shores of northern countries. Mya arenaria of our own coasts is largely eaten in some parts of Europe and North America.
Fig. 34.
British Gaper (Mya truncata).
a, foot; b, siphon-sheath; c, exhalant siphon; d, inhalant siphon; e, umbones or beaks; f, anterior, g, posterior end of shell.
Case 198.
The Corbulæ (Case 198) have one valve larger than the other and are like little Myæ, but the valves are almost closed and their siphons are very short.
