Early Miocene; Extinct.
Original Description (from Dall, 1898, p. 733-734):
"Upper Oligocene of the Chipola marls, lower bed at Alum Bluff, and the silex beds at Ballast Point, Tampa Bay, Florida; Dall and Burns.
Shell solid, rounded, plump, with fifteen to seventeen strong, rounded ribs with narrower interspaces which arc almost channelled, both ribs and channels with continuous fluctuated, sometimes crowded, low concentric lamellae; the ribs faintly grooved distally on top; the concentric sculpture sometimes strong on three or more ribs and almost absent on the intervening ones; hinge-line wide, ears large, with conspicuous but not deep notch, with six or seven coarsely imbricated, close-set radial threads on the byssal car and more numerous threads on the others; submargins nearly smooth; cardinal crura strong; inner basal margin with strong, short flutings, obsolete above. Alt. 25, lat. 25, length of hinge-line 18 mm."
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