70 POLYGYRA. 



|appets small, the right one long, giving off a short ascending branch 

 behind the lung-pore ; left lappet very small, short. 



Genitalia completely lacking accessory organs ; retractor and vas 

 deferens inserted at the apex of the penis. Spermatheca oval or 

 oblong, situated upon a short simple duct (pi. 30, fig. 6, P. troost- 

 iana; pi. 30, fig. 12, P. inflecta; pi. 30, fig. 20, Rclausa-, pi. 31, 

 fig. 27, P. spinosa ; pi. 21, figs. 12-16, P. albolabris^ The penis 

 is divided internally into two parts: (1) a lower, .invertible portion, 

 the inner surface of which shows few or many longitudinal folds, 

 which are smooth and may be either weak or strong and acute ; and 

 (2) an upper portion the cavity of which has finely corrugated walls 

 and is partially filled by one or two fleshy pillars adherent along 

 the sides. 



Jaw arcuate, solid and strong, sculptured with 7 to 20 strong con- 

 vex ribs; cutting edge without median projection, but denticulated 

 by the ribs (pi. 30, fig. 19, P. sayi Binn. ; pi. 30, fig. 21, P. kiawaen- 

 sis Simp.; pi. 21, fig. 11, P. albolabris Say). 



Distribution : North America (exclusive of some parts of the south- 

 western U. S.) ; Cuba, Bahamas and Bermuda. 



The white-lipped Helices of North America form a very distinct 

 and homogeneous genus, well distinguished by characters of the shell 

 and still more by those of the soft parts. The group, in practically 

 its present limits, was first defined in 1889, by the writer; subse- 

 quently the European forms supposed by former authors to be allied 

 to Triodopsis were shown to differ generically (Journ. de Conchyl. 

 1891, p. 22). Dr. H. v. Ihering has more recently discussed the 

 genus, under the new name, Neohelix (Zeitschr. f. wissenschaftl. 

 Zool. 1892, p. 482). This name must be considered superfluous, on 

 account of the priority of no less than twenty other more or less 

 available generic or subgeneric names proposed by various authors. 



No snails referable to Polygyra have been found in any part of the 

 Old World, or in South America, either living or fossil. It is there- 

 fore highly probable that the genus arose and developed its peculiar- 

 ities upon eastern North American soil. The West Indian species 

 are to be regarded as stragglers from the continental fauna, just as 

 Hemitrochus, Liguus and Thysanophora in Florida are emigrants 

 from the Antillean fauna. A former connection between southern 

 Florida and the Great Antilles is demonstrated by the Pliocene 

 fauna of the former; but the connection was probably not direct, 



