OF NORTH AMERICA. 425 



anteriorly a little accuminated ; columella thick, straight, outer lip with 

 a single chestnut band within." The Houghton Lake specimens were 

 submitted by Mr. Walker to Mr. E. A. Smith of the British Museum, 

 who compared them with Sowerby's types and pronounced them identi- 

 cal (see pi. XLIV. figs. 1-6). There is considerable variation in the 

 form of the shell, as is the case with mighelsi, emarginata and can- 

 adcnsis, the variation being the long or short spire, but all agree, when 

 adult, in the tightly closed umbilicus, coarse sculpture, solid shell and 

 angulated whorls. The Madison, Wisconsin, shells show a strong 

 variation toward emarginata, and certain individuals might be referred 

 to that species were it not that the majority of the specimens are of the 

 angulata type. The shells from Minnesota appear to group with angu- 

 lata rather than with typical emarginata , although isolated specimens 

 might be referred to the typical form. Dr. Stearns (Proc. Nat. Mus. 

 XXII, p. 136) records a large amount of variation in specimens from 

 Eagle Lake, Minn., collected by Mr. Vernon Bailey. These vary in 

 having a long or short spire, rounded or shouldered whorls, sutures 

 deep or shallow, aperture patulous and distorted, surface malleated 

 and shell rather solid or quite thin. The axis may be simple or rather 

 strongly twisted. An examination of these shells, in the Smithsonian 

 Institution shows them to belong to variety angulata, with a strong 

 variation toward emarginata. Nearly all specimens agree in the tightly 

 closed umbilicus although all are not angulated. 



The Michigan shells have been referred to both decollata and 

 mighelsi. They are totally unlike decollata. From mighelsi they differ 

 in the generally longer and narrower spire, rounder aperture, more 

 angulated whorls, closed umbilicus and heavier texture. Specimens 

 occur which might be referred to mighelsi, but on the whole the race is 

 distinct enough to be differentiated from mighelsi, which has not been 

 seen outside of Maine. Each race of emarginata contains many muta- 

 tions which connect it with the typical form, but this is to be expected 

 in a group of mollusks where polymorphism is as marked as in the 

 fresh-water pulmonates. 



Galba emarginata wisconsinensis (Baker). Plate XLIV, figures 

 10-18. 



Galba emarginata BAKER, Nautilus, XXIII, p. 113, 1910. 



Lymnaa emarginata wisconsinensis BAKER, Nautilus, XXIV, p. 58, Sept., 

 1910. 



SHELL: Very large, varying from elongated to globose, inflated, 

 usually rather thin ; periostracum varying from light yellowish horn to 

 chestnut; nuclear whorls as in emarginata; sculpture as in emarginata; 



