THE NATURAL HISTORY SURVEY. 339 
Animal; Not thoroughly examined, but with a narrow, 
rounded foot, tapering, blunt-pointed tentacles and general 
blackish color. 
Radula formula: 4+-5+3+7247+44+735:+4 (3-1-3). See 
generic description (Fig. 122). 
Distribution: Eastern part of the United States from 
Michigan to Florida. 
Geological distribution: Pleistocene. 
Habitat: Inthe smaller pondsand rivers, clinging to water 
weeds and alge. 
Remarks: Nickliniana is a common little species, easily 
recognized by its narrow, turreted shell and well-rounded 
whorls. The animals are gregarious, congregating together 
by hundreds. Frequently a piece of water-cress will be found 
literally black with the shells of this species. It has been 
found only in the southern region. 
Genus SOMATOGYRUS Gill, 1863. 
“Shell: Short, thin, simply striate, distinctly umbilicated 
and with 4-6 whorls; the body-whorl subglobose, more or less 
shouldered above; the spire small and the suture impressed. 
Aperture oblique (upper part most advanced) rhombo-ovate, 
narrowly rounded in front and behind; peritreme thin and 
acute, appressed behind, below the upper angle, to the whorl, 
and with its entire margin in the same plan. Operculum sub- 
spiral, corneous, but comparatively thick and strong and with 
its inner margin convex.” 
“Animal: Foot short. Snout robust and considerably 
longer than in Ammicola. Tentacles tapering, pointed. Verge 
(of S. zsogona Say =subglobosus Say) compressed and bifid, the 
inner branch being much larger than the outer, but no longer 
than the basal part; while the outer is short, somewhat trian- 
gular and pointed, and contains the canal, which is conspicu- 
ous from its white color.” 
“The lingual dentition of the type is as follows: Rhachid- 
ian tooth short and:very broad and trilobed below, with the 
outer angles much produced and narrow; cusp armed with 
seven denticles; basal denticles four on each side, the inner- 
most largest but not reaching the inferior margin of the tooth, 
and the others gradually decreasing in size outwardly, the 
outermost being obtuse and rather a lobe than a denticle. In- 
