18 



Trans. Acad. Sci. of St. Louis. 



columella oblique, with a heavy plait across its center, run- 

 ning up into the whorl and extending to the apex; the colu- 

 mella callus is heavy, wide and spreading, and, with the 

 columella, is reflected so as to completely cover the umbilicus ; 

 umbilical region indented. 



Animal: Bluish-black or black; foot short and wide, 12.50 

 mill, long, 6.50 mill, wide; other characters as in palustris. 



the head is carried but little in ad- 

 vance of the edge of the shell (f. 

 10). 



Jaws: As usual. 



Radula formula: f^ + -f- + J ^- 



+ i + ¥■ + i + H ( 40 — 1 — 40 ) • 

 central tooth as usual ; lateral teeth 



with a subquadrate base of attach- 

 ment ; reflection large, a little longer 

 than wide; bicuspid, the inner cusp 

 very large and sub-bifid, the second 

 part represented only by a swelling 

 on the inner side of the cusp ; the 

 outer cusp is short and narrow, and pointed; intermediate lat- 

 erals and marginals tricuspid, the central cusp long, the outer 

 cusps short; as the marginals are approached the reflection 

 becomes narrow and the inner cusp is placed nearer the top 

 of the tooth ; marginal teeth long and narrow, of the usual 



type (f. 11). 



Distribution: Northern United States and Canada, from 

 the Atlantic to the Pacific. 



Geological Distribution : Pleistocene; Loess. 



Habitat: Found plentifully in creeks, ponds, lakes and 

 rivers, attached to pieces of floating wood, submerged vegeta- 



Fig. 10. Mouth parts of 

 Limnaea reflexa Say. A, 

 superior jaw; B, lateral 

 jaws; C. radula; D. lips. 



