Early Miocene; Extinct.
Original Description (from Dall, 1903, p. 1275):
"Oligocene of the Chipola marl, Calhoun County, Florida, Burns; and of White Beach near Osprey, Florida, Dall.
Shell ovate, inequilateral, the beaks being in or at the anterior fourth lunule; hardly impressed, concentrically striate, cordate, small; escutcheon long and narrow, wider in the right valve, bordered on each valve with a strong sulcus, the ligament hidden by the right-hand portion; sculpture of numerous narrow, elevated, thickened, concentric lamellae, somewhat reflected and with narrower concentrically striate interspaces; these cross fine radial riblets, which are distinct and uniform on the young shell but rapidly become obsolete, though the broad tops of the concentric sculpture are crenulate or, more strictly speaking, articulated by the development on them of channels or sulci corresponding to those of the obsolete riblets; hinge strong, the larger cardinals deeply bifid, the anterior lateral small and pustular; pallial sinus small, ample, short, rounded in front; inner basal margins minutely crenulate. Length of figured valve 66, height 58, double diameter 40 mm.; length of an internal cast from White Beach 75, height 60, diameter 42 mm.
This fine species is quite distinct from any of the others; the radial sculpture, contrary to usage, is more distinct in the middle of the disk than on the distal portions of the shell. It much more nearly resembles the recent west American C. multicostata Sowerby than any species now living on the Atlantic side, and adds in this way an interesting item to the list of those which indicate more or less clearly a tolerably close connection between the two faunas in Oligocene times."
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