Dae THE CHICAGO ACADEMY OF SCIENCES. 
bicuspid, the inner cusp very large, the outer cusp very small; 
there are g 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-I-60 teeth and Professor Morse 
40-1-40. (Vide Amer. L.S., p. 389.) 
Genttaha: Not examined. 
Distribution: Northern and Middle United States and 
Southern Canada; west to Manitoba and south to Georgia. 
Geological distribution: Pleistocene; Loess. 
Hatitat: Found about marshy regions, on the stems of 
water-plants and about wet stones and wood. Frequently 
found on the leaves of flags (Js) and on lily pads (Wymphea). 
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 ina 
mass of thin, transparent gelatine, at the foot of aquatic plants. 
These gelatinous masses are very numerous ...... inthe 
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 bya 
parasite (Leucochlonidum paradoxum) which sometimes modifies 
the eye-peduncles. This parasite changes into Distoma macros- 
tomum in birds. Retusa is universally distributed throughout 
the area. 
; ies rat 
ans Sale ius alae 
