THE NAUTILUS. 125 



Yet such donations as specimens of shells, shell fancy-work, books, 

 papers and pamphlets which have descriptions or pictures of shells, 

 etc., will heartily be welcomed. They shall be arranged in cases in 

 the museum, carefully preserved and duly credited to the donors. 

 Kyoto., Japan. 



A NEW VAEIETY OF LYMNAEA STAGNALIS. 



BY FRANK C. BAKER. 



{Concluded from page 113). 



Remarks : Lymnsea slagnalis lUlian<B may be known by its short 

 spire, long and narrow aperture, and compressed body-whorl. It was 

 at first thought to be a form of sanctaemariae, but a comparison with 

 that species shows it to be uniformly narrower with compressed body- 

 whorl, and more acute spire. In sanctaemariae the bodj-whorl is 

 always very rotund ; the aperture is also roundly ovate, while in 

 lillianae it is elongate-ovate. The musculature of the male organ is 

 also quite different from sanctaemariae, and similar to that of ap- 

 pressa. Lillianae differs from appressa in its siiort spire, flattened 

 and compressed body-whorl and elongated aperture. It appears to 

 be a distinguishable race of L. stagnalis. 



No true appressa were found associated with this race in Toma- 

 hawk Lake. There were a few specimens with spires and aperture 

 of equal length, showing clearly that the race is a modification of the 

 appressa type, caused, doubtless, by a change of environment. 



At Isle Royale, in Lake Superior, a form of stagnalis occurs 

 which at first sight appears quite distinct. A number of individuals, 

 however, approach very closely to var. lilliance and they may be re- 

 ferred provisionally to this race. Judging from the material at hand, 

 this is a transition form between appressa and lilliance, representing, 

 perhaps, one of the stages in the evolution of the race. The Isle 

 Royale form " is characteristic of the quieter waters of the long, 

 narrow harbors which are such a remarkable feature of the Island." 

 (Walker). Typical lilliance lives on a wave-beaten shore, and this 

 precarious environment has caused the aperture to become enlarged 

 to provide for the larger foot to enable it to retain its hold on sub- 

 merged objects. The Isle Royale form, living in quieter water, has 

 not developed the large aperture of the Tomahawk Lake shell. 



