222 THE CHICAGO ACADEMY OF SCIENCES. 



bicuspid, the inner cusp very large, the outer cusp very small; 

 there are 9 pure lateral teeth, followed by several modified 

 laterals with two very small outer cusps; marginals wider than 

 long, five-cuspid, the inner cusp small, the next large and the 

 three outer cusps small; all of the teeth are provided with 

 cutting points. The number of rows varies from 70 to 80 (Fig. 

 56). Mr. Binney found 60-1-60 teeth and Professor Morse 

 40-1-40. (Vide Amer. L. S., p. 389.) 



Genitalia: Not examined. 



Distribution: Northern and Middle United States and 

 Southern Canada; west to Manitoba and south to Georgia. 



Geological distribution ; Pleistocene; Loess. 



Habitat: Found about marshy regions, on the stems of 

 water-plants and about wet stones and wood. Frequently 

 found on the leaves of flags (Iris) and on lily pads (Nymphaa). 



Fig. 56. 



Radula of SUCCINEA RETUSA Lea. (Original.) c, central tooth; 1, 

 first lateral, 11, intermediate lateral; 40, twenty-eighth marginal; J, jaw. 



Remarks: A species easily distinguished by its narrow, 

 conic shell and straight aperture. Mr. Binney says: "It de- 

 posits its eggs, to the number of about twenty, enveloped in a 

 mass of thin, transparent gelatine, at the foot of aquatic plants. 



These gelatinous masses are very numerous in the 



warm days of June. The eggs are oval and transparent." The 

 writer has observed these egg-masses about the middle of 

 June. This species, like others of the genus, is infested by a 

 parasite (Leucochloridum paradoxum) which sometimes modifies 

 the eye-peduncles. This parasite changes into Distoma macros- 

 tomum in birds. Retusa is universally distributed throughout 

 the area. 



