422 THE CHICAGO ACADEMY OF SCIENCES. 



Limnaa mighelsi WALKER, Nautilus, XIV, p. 8, 1900 ; XXI, p. 63, 1907. 



Lymnaa emarginata mighelsi WALKER, Nautilus, XXIII, p. 9, 1909. 



Limnaa decollata CHADWICK, Wis. Nat. H. Soc., IV, p. 80, 1906. 



Limnaa emarginata LAPHAM, Proc. Phil. Acad., p. 155, 1860. BINNEY, 

 L. & F. W. Sh., N. A., II, p. 53, 1865 (part). SARGENT, Nautilus, IX, p. 127, 

 1896. WISWALL, Nat. Sci. Journ., I, p. 48, 1897. BAKER, Bull. Chi. Acad. Sci., 

 II, p. 212, pi. 1, fig. D, 1900; Bull. Chi. Acad. Sci., II, p. 195, 1900 (part). 

 STEARNS, Proc. Nat. Mus., XXII, p. 136, 1900. CHADWICK, Bull. Wis. Nat. H. 

 Soc., IV, p. 82, 1906. 



Limnea emarginata LAPHAM, Trans. Wis. State Ag. Soc., II, p. 368, 1853. 



SHELL: Solid, rotund, tumid; periostracum, light horn, varying 

 to brownish or purplish; sculpture as in emarginata, but growth lines 

 coarse, the surface of the shell frequently raised into ridges, sometimes 

 giving a malleated aspect; spiral lines rather conspicuous; nuclear 

 whorls rather large, rounded, whitish, the outline resembling those of 

 catascopium; whorls 5 to 5^, rounded, tumid, the body whorl usually 

 very convex ; the whorls increase very rapidly in size and are generally 

 strongly angulated on the shoulders of the penultimate and body 

 whorl; spire short, tumid, wide; sutures impressed; aperture ovate, 

 langer than the spire, rounded and effuse anteriorly, angulated poster- 

 iorly ; outer lip with a slight varical thickening within ; inner lip broad, 

 reflected, closely appressed to the shell, generally completely closing the 

 umbilicus; the parietal callus is very thick and in old shells is raised 

 so as to make the aperture continuous ; the columella is much thickened 

 and frequently develops a strong plait ; axis slightly twisted. 

 Length. Width. Aperture length. Width. 



22.50 14.10 14.00 8.50 mill. Lake Houghton. 



23.00 15.00 13.00 7.75 " 



21.00 13.50 14.00 7.50 " " " 



19.00 13.00 11.50 7.50 " 



18.00 13.50 11.50 8.00 " 



19.00 12.50 12.50 7.00 " Madison, Wis. 



25.50 15.50 16.00 8.25 " Pine Lake, Mich. 



23.50 16.00 17.00 8.50 " " " 



20.00 13.00 14.50 7.50 " ' " " 



TYPES : British Museum Natural History, London, England. 



TYPE LOCALITY: North America. (Probably founded on Michi- 

 gan specimens). 



ANIMAL: Not examined alive. 



JAW : As in emarginata. 



RADULA: (PI. IX, fig. H.) Formula gLV+^-T+f+T+lH-s-T+s-S 

 (31-1-31) ; the teeth are in all respects like those of emarginata. In 

 one specimen there were ten instead of nine full laterals, and the transi- 

 tion teeth began very abruptly. 



