Early Miocene; Extinct.
Original Description (from Dall, 1900, p. 1083-1084):
"Oligocene marl of the Chipola River, Calhoun County, Florida; Burns.
Shell moderately large, solid, inflated, slightly oblique, subequilateral; beaks high and rounded; sculpture of thirty-four triangular radial ribs, on the summit of which is developed a thin elevated keel of which the summit is somewhat like the top of a T-rail, overhanging at the sides, when intact, and flattened and smooth on top; the sides of the keels and ribs, up to the twenty-second, are vertically striated and sparsely sprinkled with minute granules; the posterior twelve ribs are asymmetrical, the keels being placed behind the summits of their sustaining ribs and crenulate or surmounted by obliquely set transverse nodules; the first nine ribs are somewhat similarly imbricate or nodulous, and ventrally in adults near the margin are often pressed over backward and strongly transversely wrinkled with their interspaces flat and rather wide, while over the disk the interspaces are chiefly narrow and V-shaped; different individuals show minor modifications of these details of ornament; interior with the margins fluted, the posterior margin deeply serrate, the internal face with shallow grooves extending upward from the flutings; hinge normal. Alt. 50, Ion. 40, diam. 36 mm.
This profusely ornamented species is naturally usually more or less defective, but under all conditions is a remarkable shell."
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