inhabiting the United States. 389 
on the outer side of the whorl, are two prominent 
white teeth, the lower near the base conical, the 
upper more compressed and placed farther within ; 
columella with an oblique tooth or fold projecting 
toward the centre of the aperture, and connected by 
slightly-raised curved lines of callus with the supe- 
rior and inferior extremities of the lip; base of the 
shell showing about one and a half volutions of the 
spire. 
Greatest transverse diameter more than one third 
of an inch. 
GEOGRAPHICAL DISTRIBUTION. Found hitherto in 
Illinois, Ohio, Alabama, Kentucky, and Tennessee. * 
Though not common, it seems to be a Wily apes 
species. 
Remarks. This peculiar and interesting shell has 
been hitherto rare in collections, and is therefore but 
little known. Some specimens are entirely flat on 
the upper surface, in some the strie of the whorls 
are distinct on the upper and lower surfaces, in others 
only on the upper, leaving the lower surface smooth. 
The outer whorl is occasionally carinated. 'The 
aperture is usually shaped like a horseshoe. ‘The 
teeth within the aperture might escape notice if not 
looked for. ‘The columellar tooth varies consider- 
ably, being in ‘some thin and oblique, connected by 
‘delicate lines of callus at either extremity with the 
lip, in others larger and more prominent, with the 
space between the two lines of callus more or less 
filled up with testaceous matter. This species was 
first described by Mr. Say, as Potyeyra plicáfa. A 
variety differing in some slight particulars, but found 
^ 
