394 PROCEEDINGS OF THE ACADEMY OF [1892. 



In America, the genus Helix is restricted to the West Coast" 

 until Mexico is reached, where the species sj^read over the middle 

 portion also. In South America the species are sparsely distributed. 

 I/ysinoe is the most prominent subgenus, including the larger Mex- 

 ican and Californian species. Epiphyagmophora occurs in South 

 America ; and the West Indian Eurycampta may perhaps belong 

 here. Among the fossil forms may be mentioned the section Glypt- 

 erpes Pils., proposed for Helix veterna M. & H. 



The writer has elsewhere^^ expressed the opinion that the Ameri- 

 can forms of true Helix reached this continent from Asia by way 

 of a land bridge in the region of Beiing Sea. 



Subgenus GONOSTOMA Held. 



Differs from Helix in the less comj^lex genitalia and the white- 

 lipped shell. 



Genus LEUCOCHROA Beck. 



This genus is allied to the restricted genus Helix in genitalia and 

 dentition ; it differs in having the jaw entirely smooth, with a low 

 median projection. The characters separating it from Helix are 

 not great, and have generally been much overestimated. It has 

 often been said to be near Zonites, but this supposition is utterly 

 without foundation. The species are maiuly circum-Mediterranean, 

 the best known being the common L. candidissima. 



Genus ALLOGNATHUS I'ilsbiy. 

 Man. of Conch, (2), iv, j). 121, 149, 1888. Kobelt, Nachr. bl. D. M. Ges. 1891, p. 140. 



Genitalia : 9 system provided with two digitate glands each two- 

 fingered ; dart-sack having a four-bladed dart ; duct of the recep- 

 taculum seminis bearing a long diverticulum. $ system having 

 a long flagellum. 



Jaw entirely smooth, slightly projecting in the middle. 



Radula very large ; teeth all of the same form, Avhich is that of 

 a semicircularly curved strap.'^ 



The genital system is that of Helix s. str., resembling Cavipylcea 

 as much as anything ; but the smooth jaw and especially the 

 extremely peculiar dentition, are sufficient to give generic rank. 



"See Proc. Acad. Nat. Sci. Phila., 1888, p. 193. 

 i^Check-list of Amer. Land Shells, p. 195. 

 i^See Schuberth, Arch. f. Naturg. 1892. 



