Baker — A Revision of the Limnaeas of Northern Illinois. 9 

 4, LiMNAEA HUMiLis Say. 



PI. I. f. 14. 



Limnaea humilis Say, Jour. Phil. Acad. 2 ; 378. 1822. 



Limnaea parva Lea, Proc Amer. Phil. Soc. 2: 33. 1841. 



Limnaea curta Lea, 1. c. p. 33. 1841. 



Limnaea exigua Lea, 1. c. p. 33. 1841. 



Limnaea griffithiana Lea, 1. c. p. 33. 1841. 



Limnaea linsleyi De Kay, Moll, of New York. 72. pi. iv. f. 74. 1843. 



Limnaea /econfii Lea, Proc. Phil. Acad. 1864: 113. 



Shell: Thin, transparent to translucent, ovate-conic ; color 

 light horn, sometimes reddish; surface shining, covered with, 

 numerous crowded lines of growth, which are not much ele- 

 Tated and which disappear on the apex; whorls 5, well- 

 rounded, the last being a trifle longer than the spire in most 

 specimens; spire obtusely conic; sutures impressed, some- 

 times indented; aperture oblong-ovate, somewhat expanded^ 

 narrowed at the upper part, generally a little longer than the 

 spire; peristome thin, acute; columella oblique, covered with 

 a thin testaceous deposit; the columella is reflected along the 

 lower third, the reflection nearly covering the umbilicus which, 

 is narrowly open. 



Length 8.50; width 4 00; aperture length 4.60 i width 2.76 mill. (10488.) 

 '* 8.00; '^ 4.50; " " 4.50; '' 2.25 " ^10488.) 



•* 7.25; " 3.50; " " 3.75; *' 2.00 " (10488.) 



Animal: In general form similar to desidiosa; color light 

 brown or blackish, lighter on the foot, translucent about the 

 edges of the body. Heart situated as in the last species,, 

 pulsations regular, 140-146 per minute. 



Jaw: As usual. 



Eadula formula: i^ + ^ + l + i + | + i+i| (22— 1 — 

 22); central tooth as usual; lateral teeth bicuspid, the inner 

 cusp very long and wide, 

 bifid, the outer cusp 

 smaller ; marginal teeth 

 long and narrow, the dis- 

 tal end four- cuspid, and 



two small denticles on the C ^^ i *^ ^ 5- 



center of the outer mar- Fig. 5. Eadula of Limnaea humilis Say. 

 gin {f. 5), A second C, central tooth; 1, first lateral; 15^ 

 example gave 15 — 1 — 15 °^°*^ marginal. 

 teeth with six laterals. This latter was probably an incom- 



