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: ^+^++ T i T +i.+ 1 yj-x(3_i_ 3 ). See 

 generic description (Fig. 122). 



Distribution: Eastern part of the United States from 

 Michigan to Florida. 



Geological distribution: Pleistocene. 



Habitat: In the smaller ponds and rivers, clinging to water 

 weeds and algae. 



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 SOMATOQYRUS 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 Amnicola. Tentacles tapering, pointed. Verge 

 (of 5. isogona Say= sub glob >osus 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- 



