Late Pliocene to Early Pleistocene; Extinct.
Original Description (from Dall, 1898, p. 731):
"Caloosahatchie Pliocene marl of the Caloosahatchie River and Shell Creek; Willcox and Dall.
Shell moderately large, with four principal ribs and sometimes a subsidiary, much smaller, rib at the inner edge of the submargins; backs of the ribs strongly radially striated or even threaded, the interspaces smooth or with only obsolete traces of striation, equal to or wider than the ribs; concentric sculpture usually weak, of close-set concentric elevated or incremental lines; submargins wide, the outer margins smooth, the inner threaded like the backs of the ribs; ears large, triangular, widest at the cardinal margin and pointed at the distal cardinal angle, their sculpture radial, not crowded; feeble, except upon the byssal ear, where the threads are strong and concentrically scabrous; byssal notch wide, shallow, the fascicle conspicuous; ctenolium distinct; interior reflecting the external ribs; hinge with the crura present but feeble in the young; the old specimens have them obsolete, but on the cardinal margin a relatively broad ligamentary area is formed. Alt. 83, lat. 80, diam. 30 mm.
This is one of the finest and most characteristic species of the Pliocene, remarkable for its wide, acute ears, and for having the interspaces of the ribs nearly smooth, although the ribs are striated."
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