Early Miocene; Extinct.
Original Description (from Dall, 1900, p. 1104):
"Oligocene marls of the Chipola River, Calhoun County, Florida; Dall and Burns.
Shell small, oblique quadrate, plump, rounded in front and especially on the anterior basal margin, truncate and slightly alate behind; beaks high, involute and prosogyrate; body with eleven broad, flat, rapidly widening low ribs separated by narrow interspaces in which the cross-grooves are so wide that their interspaces appear as narrow, elevated, concentric threads; ribs on the truncation seven or eight, smaller and more crowded; when perfect the ribs are surmounted by small pustules, oblong in a transverse sense on the body and drop-like in a vertical sense on the truncation; internal margin fluted, hinge normal, strong, with very deep sockets and conical teeth. Alt. 13, Ion. 9.5, diam. 10 mm.
In measuring these oblique species the altitude is taken from the point of the valve below to the top of the umbo. This shell much resembles the Caloosahatchie species, but is squarer, with the hinge-margin more produced behind and with pustules of a more transverse and different shape."
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