168 THE CHICAGO ACADEMY OF SCIENCES. 



small cusp appearing on the outer edge of the reflection above the 

 ectocone in the eleventh tooth; marginal teeth beginning abruptly, 

 much longer than wide, multicuspid, the distal extremity becoming 

 serrated. 



The marginals show great variation in the number, shape and 

 position of the distal cusps. In the Mollusca of the Chicago area the 

 lateral teeth are described as bicuspid, but this is an error, as all sub- 

 sequent examinations have shown the radula to be tricuspid. In one 

 membrane the first lateral was abnormal in having two small cusps 

 above the entocone. Nearly all of the first laterals in this membrane 

 were of this abnormal form. 



Genitalia: (Plate X, fig. B) Male organs: Penis-sac large, 

 cylindrical ; penis short, less than one-half the length of the penis-sac ; 

 vas deferens twice the length of the penis-sac ; prostate portion of vas 

 deferens about half as long as vas deferens, enlarged at its point of 

 junction with the prostate; prostate long, narrowly cylindrical, proxi- 

 mal portion globular, with a scarcely perceptible constriction behind, 

 where it again enlarges to form the cylindrical portion; this becomes 

 narrower and forms a short ribbon-like body which connects with the 

 uterine portion of the oviduct; protractor muscles always five in 

 number (seven specimens examined), two posterior and three anterior; 

 retractor muscles three in number (generally uniform), inserted in 

 the columellar muscle; the penis retractor is inserted in the posterior 

 retractor of the penis-sac, generally near its insertion in the columellar 

 muscle ; in several cases short muscles connect the penis and penis-sac. 

 The penis nerve enters the head of the penis near the insertion of the 

 penis retractor. 



Female organs : Vagina very short ; lower portion of oviduct very 

 wide ; receptaculum seminis roundly pear-shaped, its duct very narrow 

 and nearly as long as the vas deferens, and much longer than the free 

 portion of the oviduct; albuminiparous gland and second accessory 

 albuminiparous gland not essentially different from these organs in 

 Lymncea stagnalis; first accessory albuminiparous gland very large, 

 rounded and much wrinkled. The organs are usually yellowish or 

 whitish ; the receptaculum seminis is bright orange in color. 



The retractor muscles of the penis exhibit some variation (plate 

 XIV, fig. C), especially in the location of the insertion of the penis 

 retractor in the posterior penis-sac retractor, which location may be 

 near the penis (4) or near the columellar muscle (1). One specimen 

 (2) had the termination of the anterior retractor inserted in the pos- 

 terior retractor near its junction with the penis-sac. In a third indi- 



