Baker — A Revision of the Limnaeas of Northern Illinois. 3 



ered with rather coarse growth lines, and encircled by im- 

 pressed spiral lines ; whorls 4, rounded, rapidly enlarging, 

 the last one three times the size of the rest of the shell ; spire 

 sharply conic, rather short; apex small, very dark brown; 

 sutures impressed, aperture ovate, dilated, expanded at the 

 lower part ; the aperture varies from long and narrow to wide 

 and somewhat expanded; peristome thin, acute; columella 

 narrow, twisted; terminations of peristome connected by a 

 thin callus; umbilicus generally closed but sometimes very 

 narrowly perforate where the callus is not fully developed ; 

 the columella is so thin and narrow that a view may be taken 

 from the base nearly to the apex, as in Succinea retusa. 



Length 16.00; width 8.50; aperture leogtb 11.40; width 6.00 mill. (10440.) 

 " 14.00; " 7.75; " '' 9.50; '' 5.60 " (10440.) 



Animal: Almost transparent, with a short, wide foot, 

 bluntly rounded behind ; head separated from foot by a con- 

 striction, wide, bifurcated; tentacles short, thick, triangular, 

 transparent; eyes black, situated on small prominences at the 

 inner base of the tentacles; color dirty white, darker on the 

 body which is covered with white spots, seen through the 

 transparent shell; edge of mantle transparent, simple; head 

 above lilac-tinted ; respiratory orifice on right side of body, 

 near the junction of the upper part of the columella with the 

 body whorl ; the head is not much in advance of the edge of 

 the shell when the animal is in motion ; the aperture appears 

 much too large for the shell. The heart is situated on the left 

 side of the animal, as in desidiosa. The pulsations are rather 

 irregular, three or four 

 being quick, then fol- 

 lowed by a pause; they 

 vary from 53 to 60 per 

 minute. Length of foot 

 8.00; width 5.50 mill. 



Jaws: Three, the medi- 

 an elliptical, smooth, the 

 , ^ , . . , Fig. 1. Jaws of Limnaea columella Say. 



lateral jaws irregular; 



finely striated ; cutting edges brownish black, shading into 

 yellowish brown as the base of the cartilage is reached 



