Early Miocene; Extinct.
Original Description (from Dall, 1898, p. 758-759):
"Chipola beds on the Chipola River; lower bed at Alum Bluff, Chattahoochee River; Alum Bluff beds at Oak Grove, Santa Rosa County, and the Ballast Point silex beds, Tampa Bay, Florida.
The type form of this species has a relatively small number of spinose ribs, the intervening ones being free from spines, longitudinally finely striate, and show when very perfect minute scales. The adult shell is rather short and rounded and less inflated than usual in the genus. The species is remarkable for its small hinge-area.
In the variety chipolanus Dall there is no radial striation on the interspatial ribs, but rather a concentric sculpture; there are many more spinose ribs, the shell is more oval and more inflated, and, as far as the material goes, seems to attain a larger size. It may prove distinct with more perfect specimens, in which case the varietal name may be taken as specific."
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