LYMNZID OF NORTH AMERICA. AL 
Journ. Conch., I, p. 286, 1865——Tryon, Amer. Journ. Conch., III, p. 196, 1867.— 
Goutp, Ed. Binney, p. 474, figs. 726, 727, 1870.—Datt, Proc. Bost. Soc. N. H., 
XIII, p. 248, 1870—Tryon, Con. Hald. Mon., p. 91 (65), pl. 16, figs. 6-8, 1872.— 
Jerrreys, Ann. Mag. N. H., iv, X, p. 247, 1872; Journ. Conch., I, p. 16, 1874.— 
Amer. Nat., XVII; p. 203, 1883.—WEsT., Vega-Exp., IV, p. 165, 1885.—STEARNs, 
Proc. Nat. Mus., XIV, p.-101, 1891—Taytor, Ottawa Nat., VI, p. 35, 1892.— 
NyYLANnpeER, Nautilus, XV, p. 127, 1901 (part). 
Neristoma ampla Tryon, Amer. Journ. Conch., I, p. 247, 1865. 
Radix ampla Morse, Journ. Port. Soc. N. H., 1, p. 42, 1864 (part); Bull. 
Essex Inst., XII, p. 172, 1880 (part). 
Limnea mighelsi BINNEY, Land & F. W. Sh. N. A., II, p. 31, foot note, 
1865.— Baker, Shells of Land & Water, p. 12, fig., p. 35, fig., 1903. 
Lymnea mighelsi Baker, Amer. Nat., XXIX, p. 673, fig. 5, 1905—\LEr- 
MOND, Shells of Maine, p. 38, 1908. 
Lymnea (Radix) mighelsi Dati, Mollusks, p. 68, 1905 (part). 
Limnea emarginata mighelsi NYLANDER, Nautilus, VIII, p. 126, 1895 (part). 
Limnea emarginata var. mighelsi NyLANvDER, Nautilus, XI, p. 10, 1897 
(part); Nautilus, XIII, p. 104, 1900 (part) —Baxker, Bull. Chi. Acad. Sci, HU, 
p. 196, pls. 2-6, 1900 (part).—NyLANoperR, Distr. of., pls. 2-4, 1901 (part).— 
Baker, Moll. Chi. Area, pl. 33, 1902. 
Limneus mighelsianus CLEssIn, Kuster, Conch. Cab., p. 401, 1886. 
SHELL: Large, generally rather thin, ranging from ovate to very 
globose, suboval, inflated, periostracum horny, olivaceous green or rich 
chestnut; the epidermis is frequently eaten away by the carbon di- 
oxide (CO2) in the water, and is sometimes streaked as in emarginata; 
nucleus consisting of 1% chestnut or wine-colored whorls, smooth and 
rounded and rapidly increasing in size; surface dull to shining, sculp- 
ture as in emarginata; frequently, large specimens have a number of 
raised spiral ridges, and in very old specimens that last whorl is 
“humped” in several places; whorls 5-51%4, tumid, convex, inflated, 
shouldered, the last very large, flaring and strongly shouldered; spire 
flattened and much depressed ; sutures strongly impressed, deeply chan- 
nelled in some strongly shouldered forms; aperture very large, flaring, 
long-ovate, occupying from two-thirds to three-quarters the length of 
the shell, rounded below, and either rounded or square above when 
strongly shouldered, color varying from deep chocolate to bluish- 
white; peristome sharp, thin, generally not flaring; inner lip elevated 
and reflected over the umbilicus, leaving a distinct umbilical opening 
which is strongly emargined by the inner lip; the columellar callus 
spreads over the parietal wall; the lower part of the aperture some- 
times becomes so distorted that it spreads far beyond the umbilicus; 
axis twisted, forming a rather heavy plait. The juvenile shells are 
very globose and gracefully rounded, the strongly shouldered whorls 
only appearing in nearly adult or old individuals. 
