Early Miocene; Extinct.
Original Description (from Dall, 1903, p. 1389):
"Oligocene of the Chipola beds at the Chipola River and of the lower bed at Alum Bluff on the Chattahoochee River; upper Oligocene of the Oak Grove sands, Oak Grove, Santa Rosa County, Florida, Burns; Pliocene of the Brunswick Canal, Georgia, and of the Caloosahatchie beds of Florida.
Shell solid, subcircular, rounded in front and behind, equilateral, with inconspicuous beaks; sculpture of concentric incremental lines and an arcuate excavated sculpture (common to the genus and somewhat variable in minor detail in the species) as figured, and some obscure irregularly radial impressions on the anterior slope; lunule in the right valve short, small, rather broad; in the left valve none or hardly any; escutcheon none; resting stages variable, not conspicuous; hinge with strong cardinals and faint traces of the laterals, of which the right anterior lateral is best developed. Alt. 17, Ion. 19, diam. 10 mm.
This species is especially characterized by its lunule, by the rounded, not angular, ends of the hinge-line, the absence of any denticulation of the margins due to the excavated sculpture, and the extremely fine crenulations of the rather broad margins.
Absent during the cold-water period of the Miocene, this form appears to return with the warmer Pliocene waters, again to disappear finally with the renewed cooling off of the waters in Pleistocene time."
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