142 THE CHICAGO ACADEMY OF SCIENCES. 
narrow and acute, the ectocone short, spade-shaped and placed rather 
high on the reflection; the sixteenth to nineteenth teeth develop a very 
small cusp just above the ectocone ; intermediate teeth three in number, 
the entocone arising by a splitting of the mesocone (20, 21), the ecto- 
cone becoming very small and a second cusp developing on the reflection 
just above it. First marginal teeth 4-5 serrate distally, with a small 
ectocone. The typical marginal teeth are narrow and elongated with very 
small cusps (32,34). The extreme outer marginals are small, narrow 
and indistinctly serrated distally (38, 44). The number of teeth seems 
to vary in different individuals. The writer has counted from 46-1-46 to 
54-1-54; Binney (L. and F. W. Sh., p. 28) gives 40-1-40 and (p. 155) 
47-1-47 teeth; Bland and Binney (Am. Journ. Conch., VII, p. 161) 
gives 40-1-40. It is probable that the membrane having 54-1-54 teeth 
was abnormal. 46-1-46 is the number generally counted by the writer. 
The radula of the American stagnalis does not agree in all respects 
with European figures. Dybowski' figures the first lateral with a very 
small entocone, which has not been seen in any American specimen. 
Otherwise the figures are the same. Cooke? figures the central tooth 
as distinctly tricuspid and of the same size as the lateral teeth, obvi- 
ously an error, as no Lymnea has this type of central tooth. Binney 
and Bland* figure the laterals as they appear in this monograph, but 
the teeth are too aculeate and too much curved, a feature probably due 
to the use of photography, which does not produce accurate results 
in these small radule. 
GENITALIA (PI. X, fig. A): Male organs: Penis-sac very large, 
cylindrical, wide at penial opening and tapering toward the distal end; 
penis short, about one-quarter the length of the penis-sac ; vas deferens 
five times the length of the penis-sac; prostate duct about half as long 
as vas deferens; it is a very narrow tube until it enters the prostate, 
where it becomes pyriform; proximal portion of prostate large, bulb- 
shaped, constricted behind to form a narrow, ribbon-like organ, which 
gradually enlarges and then decreases in size where it joins the uterine 
portion of the oviduct; protractor muscles five to eight in number, two 
to five posterior and three anterior; these muscles are split at their 
extremities into many small branches where they enter the body wall, 
columella muscle and penis-sac; retractor muscles one to three in 
number, inserted in the columellar muscle; the penis retractor is in- 
serted in the posterior retractor of penis-sac and the penis nerve enters 
this muscle. In two specimens examined but one retractor was found. 
1Bull. Soc. Imp. Nat. Moscou, LIX, p. 256, tab. V, 1884. 
2Mollusea, p. 255, fig. 141. 
Sop. cit., pl. 12. 

