2. Terebratula. Twelve species.
Taken from the Anomia, and with great propriety, as its characteristic differences are very great; the perforation of the Anomia is always in the smaller valve, which is attached to the larger by a cardinal ligament, while in the Terebratula the perforation is always in the larger valve, which is connected to the smaller by teeth at the hinge. In some the valves are smooth, and in others grooved longitudinally.
Shell thin, equilateral, sub-triangular, inequivalve; one of the valves larger and more convex than the other, prolonged behind by a sort of heel, sometimes recurved, and pierced by a round hole at its extremity; frequently sloped more or less by a cleft of variable form; the opposite valve smaller, more flat, sometimes formed like a lid, having in the interior a system of support variable in form and complication in every true species; hinge limited, prominent, and formed by two articulating surfaces of one valve placed between corresponding projections of the other; a kind of tendinous ligament issuing from the sloping cleft of the shell, by which it is attached to marine bodies.
Terebratula vitrea.
T. dilatata.
T. rotunda.
T. flavescens.
T. dentata.
T. dorsata.
T. pisum.