Early Miocene; Extinct.
Original Description (from Dall, 1898, p. 634):
"Oligocene of the Chipola beds, Chipola River, Florida; Burns.
Shell small, solid, oblique, with prosogyrate beaks, somewhat impressed mesially near the apices of the valves; right valve ovate-rhombic with twenty strong, rounded, nodulous, radial ribs, separated by wider interspaces; left valve decidedly smaller, with the ribs smooth, squarish, and without nodules, except a few on some of the shorter anterior ribs; cardinal area wider in front of the beaks, narrower behind them; margins of the valves internally fluted; hinge-line short, with about twenty-two subequal vertical teeth. Lon. (of left valve) 5, alt. 4.7, diam. 5 mm.
This little shell was at first thought to be the young of a larger species, but nothing allied to it of a larger size has turned up at any locality in the formation, while its solidity gives it a mature appearance. The cardinal area differs in form from any of the known species in the adult state."
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