lymnteim: of north America. 417 



Journ. Conch., I, p. 286, 1865.— Tryon, Araer. Journ. Conch., Ill, p. 196, 1867 — 

 Gould, Ed. Binney, p. 474, figs. 726, 727, 1870.— Dall, Proc. Bost. Soc. N. H., 

 XIII, p. 248, 1870.— Tryon, Con. Hald. Mon., p. 91 (65), pi. 16, figs. 6-8, 1872 — 

 Jeffreys, 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.— Taylor, Ottawa Nat., VI, p. 35, 1892.— 

 Nylander, 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). 



Limncea 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. 



Lymncea mighelsi Baker, Amer. Nat., XXIX, p. 673, fig. 5, 1905. — Ler- 

 mond, Shells of Maine, p. 38, 1908. 



Lymncea (Radix) mighelsi Dall, Mollusks, p. 68, 1905 (part). 



Limncea emarginata mighelsi Nylander, Nautilus, VIII, p. 126, 1895 (part). 



Limncea emarginata var. mighelsi Nylander, Nautilus, XI, p. 10, 1897 

 (part); Nautilus, XIII, p. 104, 1900 (part).— Baker, Bull. Chi. Acad. Sci., II, 

 p. 196, pis. 2-6, 1900 (part).— Nylander, Distr. of., pis. 2-4, 1901 (part).— 

 Baker, Moll. Chi. Area, pi. 33, 1902. 



Limnceus mighelsianus Clessin, Kuster, Conch. Cab., p. 401, 1886. 



Shell : Large, generally rather thin, ranging from ovate to vtry 

 globose, suboval, inflated, periostracum horny, olivaceous green or rich 

 chestnut; the epidermis is frequently eaten away by the carbon di- 

 oxide (COS) in the water, and is sometimes streaked as in emarginata', 

 nucleus consisting of 1^4 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 5-5}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. 



