Original description, by Adams (1864, p. 307): "Testa cordata, tenuis, Iaevis, inflata; umbonibus parvis, subspiralibus, approximatis. Cardo (in valva sinistra) dentibus duobus inaequalibus, cum foveola angusta arcuata interposita, munitus; dente antico valde prominente, in medio angulatim flexo cum fossula antica et postica instracto, margine quadricuspidato; dente postico obliquo, arcuato, angusto, elongato, margine denticulis duobus vix elevatis instructo; dentibus lateralibus nullis. Pallii linea simplex; impressiones musculares semilunares.
This genus is proposed for the reception of a beautiful shell, of which, unfortunately, I possess but a single valve, which in general appearance most nearly resembles a Bucardia. The surface of the valve is simple, as in B. cor, but it is not covered with an epidermis. The complicated nature of what I have termed the anterior cardinal tooth, which is furnished with four prominent cusps, and is angularly bent on itself in the middle, with a triangular pit on each side, together with the absence of lateral teeth, will distinguish Callocardia from the Isocardia of Lamarck. The genus Anisocardia of M. Munier-Chalmas, founded on a fossil shell from the Kimmeridge Clay of Havre, appears to bear some resemblance to my proposed genus; but in that form the surface of the valves is radiately grooved, the anterior muscular scar projects as in Cucullaea, and the disposition of the hinge-teeth seems to be very different."
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