LYMNZIDA 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 awricularia the spire is very acute, while in mighelsi 
it is very broad and the whorls are tumid. The axis of awricularia is 
also much more strongly twisted and truly gyrate. The surface of 
mighelsi varies from the fine, delicate sculpturing so characteristic of 
the Lymnzeas 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 
wisconsinensis, 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 Lymnea 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 am- 
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 Lymnzas, 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. 
Limnea angulata Sows., Conch. Icon., XVIII, Lim., No. 47, pl. 7, fig. 47, 
1872. 
Limnea ampla Currier, Kent Sci. Inst., Mis. Pub., No. 1, 1868.—WALKER, 
Journ. Conch., II, p. 330, 1879—DerCamp, Kent Sci. Inst., Mis. Pub., No. 5, 
p. 7, 1881—Watxer, Nautilus, VI, p. 32, 1892; Rev. Moll. Mich., p. 17, 1894; 
Nautilus, IX, p. 4, 1895—Wiswa tL, Nat. Sci. Journ., I, p. 48, 1897. 
Lymnea binneyi Dati, Alaska Moll., p. 69, 1905 (part). 
Lymnea decollata Dati, Alaska Moll., p. 68, 1905 (part). 
Limnea binneyi Waker, Nautilus, VI, p. 33, 1892; Rev. Moll. Mich., 
pp. 18, 22, 1894. 
