ABSTRACT
The shell is conical, more or less depressed, and very rarely, even when growing in crowded groups, becomes cylindrical or elongated. The radii are either well developed, as in most of the species; or they are entirely absent, as in the great majority of specimens of Tetraclita porosa and serrata. Tetraclita radiata, also, has a very wide range, inhabiting the West Indies, the East Indian Archipelago, and New South Wales. Tetraclita porosa seems to feed chiefly on crustaceans: the number and size of the amphipods, isopods, and entomostracans, together with an annelid, in the stomachs of some specimens from South America, was quite surprising. The articular ridge is extraordinarily prominent; it projects, as measured from the external surface of the valve, to an amount equalling half the width of the valve in its widest part.
