Thracia similis
Original description, by Couthouy (1839, p. 150-151):
"Th. testa ovato-oblonga, aspera, albida vel cinerea, subdiaphana inequilaterali, latere postico longiore, truncato et subcompresso, angulo obtuso ab apice ad marginem infero-posticam decurrente; cardine foveola subtriangulari, valva utraque ligamento externe prominulo; intus alb, impressionibus muscularibus antice elongatis, quasi clavatis, postice rotundatis; impressio pallii postice valde excavata; an ossiculum?
Shell ovate-oblong, semi-transparent, of a greyish white, or ash color, ferruginous at the margins, moderately convex, covered with numerous pretty regular, concentric striae of increment, and feeling rough to the touch, in consequence of being covered with minute granulations, most conspicuous near the margins and on the truncated end; a very thin, grayish epidermis, strongly adherent, and hardly to be distinguished from the shell itself, extends over the whole surface; somewhat inequivalve, the right valve a little the larger and projecting beyond the left; beaks moderately prominent, inclined a little backwards, the summit of the left one acute, and fitting into that of the right valve, which is excavated to receive it; slightly gaping at both extremities, inequilateral; the posterior extremity, which in some individuals is almost twice the length of the anterior, is broadly truncated, a little narrowed, and that portion between the dorsal margin and the obtuse wave, which extends from the beaks to the lower extremity, is somewhat compressed; the anterior extremity is oval, the basal margin regularly but not very strongly curved; cardinal edge delicate, ligamentary supports short and subtriangular, showing a slight impression on their inner surface, as if an ossiculum might once have been attached to the internal ligament, which is thick and strong; the external ligament is small and slightly prominent; posterior dorsal area broad, and strongly marked, extending from the beaks nearly to the extremity. The interior is nearly pure white, not glossy, though exhibiting a slightly nacred apperance; anterior muscular impression elongated, simple, club-shaped, posterior one small and very regularly rounded; palleal impression very deeply indented posteriorly.
Length one and two-twentieths, height fourteen twentieths, diameter eight twentieths of an inch.
Inhabits the shores of Brazil.
In my collection and that of the Boston Soc. of Nat. History."