Baker — A Revision of the Limnaeas of Northern Illinois. 15 



ture roundly-ovate, more or less expanded; peristome thin, 

 acute, sometimes expanded, in old specimens thickened by a 

 heavy deposit within; the peristome is white and there is a 

 band of very dark brown which edges the callus deposit ; 

 columella oblique, reflected, with a large fold across the 

 middle, and covered by a heavy, whitish, testaceous deposit 

 which is more or less spreading; umbilicus closed by the 

 spreading callus and reflected columella, but the region is 

 indented and the umbilicus is sometimes narrowly open. 



Animal: With a short, wide foot, rounded before and 

 behind; tentacles short, triangular; color black, lighter be- 

 low, the body spotted with white which shows through the 

 shell. Heart situated as usual, pulsation regular, 80-81 per 

 minute. Length of foot 8.00, width 3.00 mills. 



Jaw; As usual. 



Radula formula: f£ + $ + f + 1 + | + £ + 1^(34 — 1 — 

 34): central tooth as usual; lateral teeth of the usual type, 

 bicuspid ; tran- 

 sition teeth at 

 first like later- 

 als but tricus- 

 pid, the central 

 cusp the largest 

 (11) but soon 

 (13) the inner 

 cusps become 

 more equal and 

 the outer cusp 

 small; marginal 

 teeth of the 

 usual type (f. 8). In one membrane examined (f. 9) the first 



m 



Fig. 8. Radula of Limnaea palustris Miiller. C, central 

 tooth; 1, first lateral; 7, seventh lateral; 11— 13^ inter- 

 mediate teeth ; 14-30 ; types of marginal teeth. 



