192 THE CHICAGO ACADEMY OF SCIENCES. 



very decided swelling on the inner side, which is probably a modified 

 entocone. The ninth tooth (transition) is distinctly tricuspid, while 

 the tenth tooth is a typical marginal, the transition being very abrupt. 



The only radula of Lymncea known which is at all comparable 

 with this species is Lymnaa hawaiensis 1 Pilsbry, described from Ha- 

 waii, in which the laterals are modified in much the same manner. This 

 species is very small and of a wholly different character and should 

 probably be made the type of a distinct group of Lymnseas. The com- 

 bination of the characters of the shell, radula and genitalia gives to 

 this species a higher rank than a subgenus or section and entitles it 

 to full generic consideration. 



Acella haldemani ("Deshayes," Binney). Plate XVIII, figure 1; 

 Plate XXVI, figures 1-1 



Lymncca gracilis JAY, Cat., Ed. 3, p. 112, pi. i, figs. 10, 11, 1839, (non Zie- 

 then, 1830). WHEATLEY, Sh. U. S., p. 23, 1845. JAY, Cat. Ed. 4, p. 269, 1852. 

 LEWIS, Proc. Phil. Acad., 1856, p. 259; 1860, p. 18. REEVE, Elements of Conch., 

 p. 179, I860. LEWIS, Proc. Bost. Soc. N. H., IX, p. 160, 1862. MORSE, Amer. 

 Nat, p. 651, pi. 11, fig. 6, 1870. LEWIS, Proc. Phil. Acad., 1872, p. 102. SMITH, 

 Nautilus, XX, p. 91, 1907. WALKER, Nautilus, XXIT, p. 18, 1908 ; Journ. Conch., 

 XII, p. 240, 1909. 



Lymnea gracilis DEKAY, Cat. An. N. Y., p. 32, 1839. JAY, Ann. N. Y. 

 Lye. N. H., IV, p. 170, 1846. CURRIER, Sh. Grand. Riv., Mich., 1859. WHITTI- 

 MORE, Proc. Bos. Soc. N. H., VII, p. 151, 1859. 



Limn&a gracilis C. B. ADAMS, Am. Journ. Sci., XL, p. 267, 1841; Thomp. 

 Hist. Vt., pt. I, p. 153, 1842. STIMPSON, Sh. N. Eng., p. 52, 1851. LEWIS, Proc. 

 Bost. Soc. N. H., V, p, 296, 1856; Proc. Bost. Soc. N. H., VI, p. 2, 1856. 

 BINNEY, Check List, p. 12, I860. LAPHAM, Proc. Phil. Acad., 1860, p. 155. 

 BINNEY, L. and F. W. Sh. N. A., II, p. 69, fig's. 113, 114, 1865 ; Journ. de Conch., 

 XV, p. 427, 1867. CURRIER, Kent Sci. Inst. Mis. Pub., No. 1, 1868. SOWERBY, 

 Conch. Icon., XVIII, Limn, sp., 19, pi. 3, fig. 19, a, b, 1872. TRYON, Con. Hald. 

 Mon., p. 114, 1872; HERON, Ottawa Nat., I, p. 39, pi. 11, fig. 4, 1880. FISCHER, 

 Man. de Conch., p. 506, 1883. TRYON, S. and S. Conch., Ill, p. 101, pi. 103, fig. 8, 

 1884. BEAUCHAMP, L. and F. W. Sh. N. Y., p. 9, 1886. Ottawa Nat., IV., p. 56, 

 1890. TAYLOR, Ottawa Nat. VI, p. 35, 1892. WALKER, Nautilus, VI, p. 34, 1892. 

 MARSHALL, Rep. N. Y. State Mus., XLVII, p. 65, 1893. WALKER, Rev. Moll. 

 Mich., p. 18, 1894. MARSHALL, Rep. N. Y. Col. Exp., p. 512, 1894. SARGENT, 

 Nautilus, IX, p. 127, 1896. WALKER, Nautilus, XII, pp. 119, 131, 1899. LET- 

 SON, Bull. N. Y. State Mus., LXXXVIII, p. 56, 1905. CHADWICK, Bull. Wis. Soc. 

 N. H., N. S. IV, p. 83, 1906. BAKER, Science, N. S., XXVII, p. 943, 1908. 

 LETSON, Bull. Buf. Soc. Nat. Sci., IX, p. 242, 1909. 



Limnea gracilis HALDEMAN, Mon. Limn., p. 50, pi. 13, fig. 21, 1842. NEW- 

 BERRY, Proc. A. A. A. Sci., V, p. 105, 1851. LAPHAM, Trans. Wis. State Agr. 

 Soc., II, p. 368, 1852. DEKAY, Zool. N. Y., p. 70, pi. 4, fig. 73, 1843. MILES, 

 Geol. Surv. Mich., 1860, p. 237. 



Limnceus gracilis KUSTER, Conch. Cab., p. 50, taf. 11, figs. 9, 10, 1862. 



1 See Proc. Phil. Acad., 1903, p. 791, for figures. 



