by William Swainson

“ Corrie of Birmingham, favoured us with two examples of what appears to be a variety of that which we have figured. The substance of both is opake; the inside white, tinged with buff, and with scarcely any pearly lustre. Inhabits North America, but we know not any precise locality. ”

“ We have now entered among the typical species, where every form occurs between a round and an ensiform shape. Leaving these, Nature proceeds to fashion an indistinct developement of Alasmodon in the species before us, where that part of the hinge plate, immediately beneath the umbones, is somewhat raised, and undulated. In A. rugosus these compressed undulations assume more the form of tubercles; and finally, in the Alasmodon marginatus of Say, the teeth are sufficiently developed to place that shell in a distinct group. ”