Early Miocene; Extinct.
Original Description (from Dall, 1900, p. 1080-1081):
"Oligocene marl of the Chipola River, Calhoun County, Florida; Burns.
Shell small, thin, inflated, slightly oblique and inequilateral, with high, well-rounded beaks, anterior end slightly shorter, general outline suborbicular; sculptured with nineteen elevated ribs of triangular section separated by narrow, cross-striated channelled interspaces, each rib surmounted by a low keel the edge of which is periodically produced into short spines each ending in a knob, sides of the ribs finely concentrically striate; near the posterior end the whole surface shows a microscopic granulation; internal margins deeply fluted; hinge normal, delicate. Alt. 20, Ion. 20, diam. 15.5 mm.
This elegant little shell is close to the young of the C. echinatum L. of Europe, in which, however, the ribs are lower, the interspaces wider and less sharply cross-striated, the keel less elevated and continuous, and the spines long and sharp. The European shell is more equilateral, with a longer hinge-line and not oblique. However, they are so similar as to be very interesting. According to Turton and Hanley, the young C. echinatum is probably the C. ciliare of Linné."
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