172 MOLLUSCA. 
The locality from whence Pfeiffer’s original specimens! were obtained is not known. 
The specific name alludes to. the clue given by Ariadne to Theseus in the Greek 
mythology ; therefore the genitive form “ ariadne” is correct. 
16. Polygyra acutedentata. 
Helix (Polygyra) acute-dentata, Binney, Proc. Acad. Phil. 1857, p. 183'; Fisch. & Crosse, Miss. 
Scient. Mex., Mollusca, i. p. 288°. 
Helix acutedentata, Binney, Terr. air-breath. Moll. of N. Am. iv. p. 28, t. 76. fig. 1°; Pfr. Monogr. 
Helic. Vivent. iv. p. 352‘; Binney & Bland, Land and Fresh-water Shells of N. Am. 1. 
p. 103, fig. 179°. . 
Dedalochila acutedentata (Binn.), Tryon, Am. Journ. Conch. iii. pp. 65, 78, t. 5 (10). figg. 11, 13 
(1867) °. 
Helix unguifera, Mousson, in some collections. 
Var. loisa. 
Helix (Polygyra) loisa, Binney, Proc. Acad. Phil. 1857, p. 183, t. 76. fig. 2”. 
Helix loisa (Binn.), Pfr. Monogr. Helic. Vivent. iv. p. 351 °. 
Dedalochila loisa (Binn.), Tryon, Am. Journ. Conch. iii. t. 5 (10). figg. 12, 14 (1867) ’. 
Helix (Polygyra) acutedentata, var. quinquedentata, Fisch. & Crosse, loc. cit. p. 289”. 
Hab. N.W. Mextco: Guaymas, Sonora‘; Mazatlan river, Sinaloa (Gumbel 1); 
Mazatlan (forrer). 
Very remarkable by the hooked and pointed shape of the middle external tooth, 
which is directed to the outside of the aperture, as a defensive weapon; and which 
has an analogue in another American species, Helix (Labyrinthus) uncigera, Petit. 
Another variety is said’ to be found in Texas ’. 
17. Polygyra anilis, 
Helix (Polygyra) anilis, Gabb, Am. Journ. Conch. i. p. 209, t. 19. figg. 1-4 (1865) *; Fisch. & 
Crosse, Miss. Scient. Mex., Mollusca, i. p. 269 *. 
Helix anilis (Gabb), Pfr. Monogr. Helic. Vivent. iv. p. 427 *. 
Polygyra anilis (Gabb), Tryon, Am. Journ. Conch. iii. pp. 158,176, t. 7 (11). figg. 17, 18 
(1867) *. 
Hab. N.W. Mexico: Guaymas, Sonora (Gabb 1). 
Very distinct. from all others of the genus by the want of an external tooth in the 
aperture. 
STROBILA. 
Strobila, Morse, Journ. Portland Soc. i. p. 26 (1864) (nec Sars, 1835, juvenile state of Medusa). 
Shell globose-conic, with thickened peristome and internal revolving lines on the 
