LYMN^IME OF NORTH AMERICA. 151 



a single small, pure white shell dredged from deep water. The lower 

 part was smashed by the dredge. The animal was pure white and 

 consequently the black eyes were very conspicuous" (in letter). 



Future search will doubtless determine whether this peculiar shell 

 is simply a case of albinism or an abyssal race of stagnalis. 



Lymnaea stagnalis perampla (Walker) . Plate XX, figures 7-9 ; 

 pi. XXII, figure 5. 



Limncea stagnalis Walker, Nautilus, VI, p. 31, pi. 1, fig. 6, July, 1892. 



Lymncea stagnalis v. perampla Walker, Nautilus, XXII, No. 1, p. 8. pi. II, 

 figs. 5, 6, May, 1908. 



This variety differs from the usual North American form, var. 

 appressa Say, by its shorter, rapidly accuminating spire and larger, 

 strongly shouldered body whorl ; the first three whorls of the spire 

 are slender and increase regularly in size; the penultimate whorl is 

 disproportionately enlarged, swollen and subangulated by the flat- 

 tening of the upper part of the whorl, which in the body whorl develops 

 into a prominent shoulder (Walker). 



Aperture 



Length. 



Breadth. 



length. 



Breadth. 





45.50 



26.00 



28.00 



18.00 mill. 



Type. 



45.00 



23.75 



26.00 



17.00 " 



" 



49.00 



26.50 



30.00 



15.50 " 



Cotype. 



Types: No. 1834, coll. Bryant Walker; cotype, Chi. Acad. Sci., 

 1 specimen No. 23921. 



Type Locality : Houghton Lake, Roscommon County, Mich. 



Animal, Jaw, Radula and Genitalia: Not examined. 



Range : Michigan. A race of the Canadian region and of the 

 Canadian life zone. 



RECORDS. 



Michigan: Douglas Lake, Cheboygan Co. (Ferriss; Velie; Walker); 

 Houghton Lake, Roscommon Co. (Walker). 



Geological range : Unknown. 



Ecology : "All the specimens of stagnalis from Houghton Lake 

 that I have seen, more than thirty, are of this peculiar form, which 

 is apparently a well marked race" (Walker). 



It is interesting to note that in Marl Lake a small enlargement of 

 Marl River, which connects Higgins and Houghton Lakes, the typical 

 stagnalis appressa was the only form found. 



Remarks : As remarked by Walker, this variety seems to be a 

 well marked race, easily separable from typical stagnalis appressa. 

 It will probably be found in other localities in northern Michigan, and 

 possibly in parts of Minnesota, Wisconsin and northern Ontario. 



