Generic Character.—See Pl. 96.
- A. testâ transversim oblongâ, crassâ, anticè compressâ, extremitate utrâque rotundatâ; umbonibus valdè prominentibus, crassis; laminâ cardinali convexâ.
- Shell transversely oblong, thick, anteriorly compressed, both extremities rounded; umbones very prominent, thick; hinge-plate convex.
This extremely rare shell bears not the least resemblance to any which Lamarck has described, or with which I am acquainted. It was formerly in the late Mr. Forster's collection, and is now in the possession of Mrs. Mawe. Its form is like that of Unio ovatus (Mya ovata of Montague), but it is a much thicker and stronger shell; the posterior end is greatly compressed, but round; the umbones convex, remarkably thick, and deeply eroded; the inside pearly and iridescent, with a strong flesh-coloured tinge; the ligamental or hinge-plate is perfectly smooth, and rather convex; the muscular impressions are deep.
One valve of the specimen above alluded to (the only one I have seen), is uncoated, and beautifully iridescent. Its country is unknown—but I think it may prove a native of the South American rivers.