Early Miocene; Extinct.
Original Description (from Dall, 1903, p. 1429-1430):
"Oligocene of the Chipola horizon on the Chipola River and at Alum Bluff on the Chattahoochee River, Calhoun County, Florida; Burns and Dall.
Shell solid, robust, obliquely oblong, the beaks full, prominent, prosogyrate, and nearly anterior; anterior side short, bluntly rounded, posterior side longer, compressed, roundly subtruncate behind; sculpture of about nineteen radial ribs, of which the posterior five or six are smaller and less elevated than the others; anterior ribs stout, sometimes with a thread or terrace laterally, the summit articulated rather sparsely with small, squarish, transverse nodules, which have a tendency to become obsolete behind and below; interspaces narrower than or subequal to the ribs, partially channelled; lunule extremely small and deeply incised; hinge normal; the anterior cardinal pustular, the interior margins with shallow flutings. Length 47, height 38, diameter 36 mm.
A remarkably fine species, abundant in the Chipola beds, and not likely to be confounded with any but the following species."
To access this description in its original formatting through Google Books, click here.