Miocene to Early Pleistocene; Extinct.
Southern Florida to Virginia.
Original Description (from Say, 1824, p. 132-133):
"Shell sinistral, subovate: inferior valve convex, with numerous convex ribs interrupted by fornicated scales at the lines of increment: hinge curving a little upward, very much contracted and short: superior valve flat, wrinkled concentrically, without any appearance of longitudinal lines: hinge more dilated than that of the superior valve, and oblique with respect to the thickness of the shell.
Length of the specimen four inches and four fifths; breadth four inches and a quarter. A large superior valve is five inches and three quarters long, and five inches and a quarter broad.
Like many species of this genus, it varies much in form, and in the prominence of the ribs on its convex valve; but these ribs are very obvious on the nine specimens under examination. Externally some varieties have a striking resemblance to O. bellovacina, Lam. but the hinge is much more contracted.
Besides those obtained by Mr. Finch, Mr. Z. Collins presented a fine specimen to the Academy, found on the west branch of the Potomac, about fifteen miles below Alexandria."
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