LYMNyEID.E OF NORTH AMERICA. 181 



The shape of the teeth vary somewhat in different membranes and 

 also in the same membrane in different positions. The radula of the 

 Lincoln Park specimens does not agree with the figure given by Hazay 

 (Mai. Blatt., N. S., VII, pi. 1, fig. 1) of European specimens, the 

 laterals being distinctly bicuspid in the Lincoln Park specimens. Many 

 examinations have been made of the radulse of these specimens with 

 powers ranging from 500 to 600 diameters and in no case could a 

 tricuspid tooth be found after the first or previous to the tenth tooth 

 as here figured. It is possible that there are two or more species of 'this 

 group distinguishable by difference in the number of the cusps of 

 the lateral teeth. The second to the ninth marginal teeth exhibit a 

 peculiar swelling on the inner edge of the mesocone, which might be 

 taken for a third cusp, if care is not used in making the examination. 

 The figure on plate VI is drawn from fresh, unworn teeth. In one 

 membrane, several of the lateral teeth exhibit a number of small serra- 

 tions on the inner margin of the mesocone. 



The radula of auricularia is peculiar in the aculeate cusp of the 

 central tooth and the tricuspid first lateral, the bicuspid laterals follow- 

 ing with the rounded swelling on the inner side of the mesocone. No 

 other species at present known has this peculiar combination of char- 

 acters. 



GENITALIA (Plate X, Fig. C) : Male organs: Penis-sac cylin- 

 drical, six mill, long and two mill, wide, diminishing in diameter toward 

 the distal end, where it swells slightly before receiving the vas def erens ; 

 penis very slender, eight mill, in length, with a rounded head; vas 

 deferens seventeen mill, in length; vas deferens to prostate six mill, 

 long, enlarging slightly as it enters the prostate; prostate roundly 

 pyriform at its proximal end, receiving the vas deferens in a little 

 depression ; the prostate narrows behind the pyriform portion and 

 forms a rather long ribbon-like organ which unites with the oviduct 

 under the albuminiparous gland ; retractor muscles of penis two in 

 number, one for the penis-sac, which widens and forms a long double 

 insertion as it joins the sac, and one narrow ribbon-like muscle which 

 extends from the columella muscle to the head of the penis ; the latter 

 is strongly reflected by this muscle ; protractor muscles four in number, 

 two narrow muscles on the posterior face and two larger muscles with 

 many branches on the anterior face. 



Female organs : Oviduct short and wide, the anterior two-thirds 

 simple and cylindrical, the posterior third, forming the uterine portion 

 much convoluted ; receptaculum seminis large, elongate-pyriform in 

 outline, with a duct 6.50 mill, long, joining the oviduct one mill, from 



