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 1 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 2 figures the central tooth 

 as distinctly tricuspid and of the same size as the lateral teeth, obvi- 

 ously an error, as no Lymn&a has this type of central tooth. Binney 

 and Bland 3 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 radulse. 



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 def erens 

 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. 



'Bull. Soc. Imp. Nat. Moscou, LIX, p. 256, tab. V, 1884. 

 2 Mollusca, p. 255, fig. 141. 

 3 op. cit., pi. 12. 



