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Cincinnati Society of Natural History. 



Heusoma camfanuutus Say. Plate IV, G. 



Radula formula ,-f f • + \ + \ L + f + If (25 - 25) J 

 central tooth as usual ; lateral teeth with three very nearly 

 equal cusps, the central cusp being a little longer than the 

 others; transition teeth and marginal teeth as usual. The 

 lateral teeth of this species differ considerably from those of 

 trivolvis, bicarinatus, and truncatus, in having three nearly 

 equal cusps. Several examinations have been made to verify 

 this statement. 



Gykaulus parvus Say. Plate IV, J. 



Radula formula ±± + f + i + i + i^ (18-1-18); central tooth 

 with a base of attachment longer than wide, produced at the 

 lower outer corners, and excavated in the center of the lower 

 margin; reflexion bicuspid, the cusps short and wide; lat- 

 eral teeth with a subquadrate base of attachment, expanded 

 at the lower outer corner, reflexion wide, tricuspid, the cen- 

 tral cusp long and rather wide, the side cusp shorter; mar- 

 ginal teeth modified laterals in being low and very wide, the 

 outer cusp splitting into 2-3-4 small cusps. A number of 

 specimens have been examined, and there appears to be no 

 variation worthy of mention. 



Segmentina armigera Say. Plate V, A. 



Radula formula fT + f + i+ f + f+ (18-1-18); central tooth 

 with a long, narrow base of attachment, expanded on the 

 lower outer corners; reflexion wide, bicuspid ; lateral teeth 

 wide, a trifle longer than wide, tricuspid, the center cusp 

 long, wide and sharp, and the side cusps short and sharp ; 

 marginal teeth at first similar to laterals, with the addition of 

 a second, small outer cusp, but becoming wide and low toward 

 the margin, and developing three small outer cusps. A large 

 number of specimens have been examined. 



Ancylus rivularis Say. Plate V, B. 



Radula formula ^ + -f { + ^ + yr* (16-1-16); the cen- 

 tral tooth is simple, as in Limncea; the lateral teeth have a 



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