LYMNJEHXX OF NORTH AMERICA. 421 



various lakes, ponds and rivers of this area exhibit examples for 

 ecological study unsurpassed by any other single region in the United 

 States. Many mutations retain certain individual characteristics which 

 distinguish them from specimens of nearby localities. Thus typical 

 cmarginata from Eagle Lake is oval with a comparatively long spire. 

 The Cross Lake specimens are quite globose, as are those from Aroos- 

 took River, Portage Lake and Fish River. The Square Lake Inlet 

 specimens are the largest and finest, with short spire and wide aper- 

 ture recalling Radix auricularia. The resemblance is, however, only 

 apparent, for in auricularia the spire is very acute, while in mighelsi 

 it is very broad and the whorls are tumid. The axis of auricularia is 

 also much more strongly twisted and truly gyrate. The surface of 

 mighelsi varies from the fine, delicate sculpturing so characteristic of 

 the Lymnaeas to a rough, malleated surface. 



Specimens from Brome Lake, Quebec, (which were previously, 

 but erroneously referred to wisconsinensis) are not quite typical, show- 

 ing a tendency to vary toward angulata. Rarely a specimen resembles 

 zvisconsinensis, but in that race the aperture is normally round, while 

 in the Brome Lake specimens it is quadrangular. 



Mighelsi is unlike any other form of Lymnaea and its broad, de- 

 pressed spire and large, elongated aperture are features sufficiently 

 characteristic to cause its separation as a race. There is some varia- 

 tion in the height of spire, showing transition to emarginata. The um- 

 bilical chink varies somewhat, being almost closed in some specimens. 

 Binney, Tryon, Dall and other conchologists have placed mighelsi in 

 the section Radix of the typical Lymnaeas, but an examination of the 

 axis shows that it is plicate and not gyrate, the animal, besides, having 

 anatomical features not embraced in Radix. Mighelsi is not related to 

 decollata Mighels which belongs to the catascopium group. 



Galba emarginata angulata (Sowerby). Plate XLIV, figures 

 1-9. 



Limnaa angulata SOWB., Conch. Icon., XVIII, Lim., No. 47, pi. 7, fig. 47, 

 1872. 



Limnaa ampla CURRIER, Kent Sci. Inst, Mis. Pub., No. 1, 1868. WALKER, 

 Journ. Conch., II, p. 330, 1879. DECAMP, Kent Sci. Inst., Mis. Pub., No. 5, 

 p. 7, 1881. WALKER, Nautilus, VI, p. 32, 1892; Rev. Moll. Mich., p. 17, 1894; 

 Nautilus, IX, p. 4, 1895. WISWALL, Nat. Sci. Journ., I, p. 48, 1897. 



Lymnaa binneyi DALL, Alaska Moll., p. 69, 1905 (part). 

 Lymnaa decollata DALL, Alaska Moll., p. 68, 1905 (part). 

 Limnaa binneyi WALKER, Nautilus, VI, p. 33, 1892; Rev. Moll. Mich., 

 pp. 18, 22, 1894. 



