Neiv or Little Knoxon North American Limnceidos. 



97 



lies upon the oviduct, extending to the vagina. The genital bladder 

 (?) or receptacidum seminis, is large, and communicates with the 

 vagina by a long duct. The vaginal aperture is small, opening on the 



T, testicle; 0, ovary ; V, oviduct; P', prostate ; G- B, receptaculum seminis ; D, its 

 duct; V, vagina ; V D, vas deferens ; P, penis; P S, penis sac; N, nerve. 



right side, behind the male orifice. I have been unable to work out 

 the circulatory system, owing to the fact that I have had but a single 

 animal from which to determine the points given, and that was an alco- 

 holic specimen and much hardened. The same is true of the relations 

 and position of the renal organs. 



The most striking thing in the anatomy of this species is its close 

 approach, in man}' of its characters, to the land snails, especially to 

 Limax. What this may indicate as to the past history of these crea- 

 tures is entirely speculative; but the relation is much nearer than that 

 of the genus P/a;ior6is to which reference has been made by several 

 authors. 



In all their habits these creatures exhibit a close relation to Physa. 

 Like them the}' can float upon the surface, shell downward; in this 

 position, by a peculiar motion of the foot, they swim slowly and awk- 

 wardly. They spin threads of mucus upon which they ascend and de- 

 scend. The upper end of the thread floats, sustained b}' a bubble of 

 mucus. In all these respects they are like Physa and other species of 

 Li77in(Ba. 



Note on the Plaxorbis glabratus, Say. 



In the Journal Acad. Nat. Sc, (vol. i., p. 280, June, 1818), Mr. Say 

 published his description of P. glabratus as follows: 



"Shell sinistral; whorls about five, glabrous or obsoletely rugose, 

 polished, destitute of any appearance of carina; spire perfectly regu- 

 lar, a little concave; umbilicus large, regularly and deeply concave; 

 exhibiting all the volutions to the summit: aperture declining, re- 

 markably oblique with respect to the transverse diameter. Breadth 

 nearly nine tenths of an inch." 



