10 THE CHICAGO ACADEMY OF SCIENCES. 



marginals show no variation, all being of the usual multicuspid type. 

 The center tooth is generally quite uniform in shape, the reflection 

 being more or less trilobed with a spade-shaped cutting point. The 

 cutting point is difficult to see except with high powers, the opaque 

 portion standing out clearly and causing the tooth to appear trilobed 

 or tricuspid, thus causing the errors mentioned below. The central 

 tooth is very difficult to observe clearly, owing to its small size. It 

 has been figured as tricuspid, trilobed and simply ovate by different 

 authors. In the Cambridge Natural History, Mollusca (Cooke, 1895, 

 p. 235) it is figured as tricuspid, the cusps being as large as those of 

 the lateral teeth, unquestionably an- error, as no Lymnaeid has this type 

 of central tooth. 



In studying these radulse it is important to consider only the newer 

 perfect teeth, as the older teeth near the mouth are usually much worn 

 and hence give a false idea of the true form of the cusps. Figure D, 

 plate III, shows two of these worn teeth. Compare these teeth with 

 the same numbered teeth in figure A of the same plate. On plates 

 VII, VIII and IX the radulae of the various species are figured. 1 



d. THE REPRODUCTIVE SYSTEM. Plates I, III, IV. 



Like all pulmonates, the Lymnaeas are hermaphrodites. The male 

 and female systems are, however, separated for the most part, the 

 opening of the male being behind the right tentacle, while that of the 

 female is at the base of the neck near the respiratory cavity. (PI. Ill, 

 fig. G>. 



The organs of the fresh-water pulmonates divide naturally into 

 three groups, as fellows : 



f penis. 



penis-sac. 

 Male organs ^ vas deferens. 



prostate. 

 t prostate duct. 



vagina, 

 oviduct. 



,-, . uterine portion of oviduct. 



Female organs 



' receptaculum semmis or spermatheca. 



duct of same. 



albuminiparoas gland. 



first and second accessory albuminiparous glands. 



Common to both.. \ votestis. 



/ hermaphorodite duct. 



*See the chapter on classification for a further consideration of the specific 

 variation of radulae. 



