Baker — A Revision of the Limnaeas of Northern Illinois. 11 



ella strong, white; reflected so as to cover the umbilicus, 

 there is a small fold crossing the center of the columella ; 

 umbilicus small, narrow, deep, covered by the reflected 

 columella. 

 Length 12.00; width 5.50 



10.50; 

 9.00; 

 11.00; 

 13.00; 

 15.50; 



5.00 

 4.50 

 5.50 

 6.00 



7.00 



aperture length 5.50 

 " " 5.00 



" " 4.00 



" " 5.50 



" " 6.00 



" " 7.50 



width 3.00 mill. (10656.) 



" 2 50 " (10656.) 



" 2.50 " (10656.) 



" 3.00 " (10437.) 



" 3.50 " (12337.) 



" 4.00 " (12687. ) 



Animal: Black or bluish black, lighter below and minutely 

 flecked with small whitish dots, which are scarcely visible, ex- 

 cept on the top of the head; head distinct; tentacle short, 

 flat, triangular; foot short and wide, 8 mill, long and 3 

 mill. wide. Heart placed a trifle below the center of the 

 columella, the pulsations ranging from 129 to 133, somewhat 

 irregular. 



Jaw: As usual. 



Radula formula: f* + 2 + | + a + £ + 2. + 11 (32—1 

 — 32 ) : central tooth as usual ; lateral teeth with a sub- 

 quadrate base of attachment, the reflection longer than 

 wide and bicuspid; the inner cusp very large, the outer 

 cusp short; the 8-10 teeth are modified from laterals to 

 marginals by the 

 bifurcation of the 

 inner cusp, and 

 the splitting up 

 of the upper part 

 of the outer cusp 

 into small denti- 

 cles ; the tenth 

 tooth is trifid on 

 the inner cusp 

 and the eleventh 

 and all that fol- 

 low are of the us- 

 ual form (f. 6). 



Distribution : New England to California and Hudson Bay 

 to Louisiana. 



Geological Distribution: Pleistocene; Loess. 



Aa 



'IX 



Fig. 6. Radula of Limnaea caperata £ay. C, central 

 tooth; 1-7, lateral teeth; 8-9, modified marginal 

 teeth; 10, first true marginal; 12, 14, 17, inter- 

 mediate marginals; 20-25, outer marginals. 



