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. 



aperture length 5.50; width 3.00 mill. (10656.) 



«< " 5.00; " 2.50 " (10656.) 



" '* 4.00; " 2.50 " (10656.) 



*' '» 5.60; *' 3.00 " (10437.) 



*♦ " 6.00; '* 3.60 «' (12337.) 



" " 7.60; «' 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. 



nadula formula: I?: +f + i + + + i + | + li (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 (/. 6*). 



Distribulio7i : 

 to Louisiana. 



Fig. 6. Eadula of Limnaea caperata Say. 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. 



New England to California and Hudson Bay 

 Geological Distribution : Pleistocene; Loess. 



