392 PROCEEDINGS OF THE ACADEMY OF [1892. 



Jaw coarsely ribbed (odontognath), finely ribbed (pyenognath), or 

 smooth (oxygnath). 



The aj^pendages of the 9 system mentioned above are developed 

 in no other group of Helices.^ 



Genus HELIX Linne (restricted). 

 Pilsbry, Proc. A. N. S. Phila., 1891, p. 313. 



Genitalia : 9 system having a dart-sack or sacks containing 

 darts, a pair of mucous glands or one, the spermatheca duct long 

 and provided with a long diverticulum ; $ system having a flagel- 

 lum upon the penis, and rarely an appendix. 



Jaw stout, strongly ribbed. Teeth of the radula normal. 



Shell various ; animal i-eproducing by many small eggs. 



Only in the more highly organized species are all the above 

 characters of the genitalia developed. In many sections of the 

 genus several of the accessory organs may be absent. I am dis- 

 posed to think that in some cases the genital system has arrived at a 

 simple condition by degeneration or loss of the accessory organs. 

 It is upon this ground that I admit Cressa West. (Pseudocam- 

 jjylcea Hesse, non Pfr.) to the genus. 



The genus is more numerous in species than any other; and a 

 large number of subgeneric and sectional groups have been institu- 

 ted for their classification. The anatomy of a great number of 

 species has been investigated, and a sufficient basis of facts is known 

 to enable us to divide the genus into several well-marked subgenera, 

 all of which are represented in the Paljearctic Region, which has 

 been, no doubt, the birth-place of this type. As it is not my pur- 

 pose to enter into the question of the subdivision of this genus 

 here, I will simply enumerate the leading groups in the several 

 geographical regions, viz. : (1) Eur-African, (2) East-Asiatic, 

 and (3) American. 



The Eur-Afric.\n area comprises the greatest variety of types, 

 both recent and fossil, and the genus doubtless originated and 

 developed its peculiarities therein. The more prominent subgenera 

 or sections are as follows : Arianta, Campylcea, Elona, Ckilotrema, 

 Isognomostoma," Pomatia, Eremina, Macularia, Tachea, Iberiis, 

 Hemicycla, Leptaxis, Plebeeula, Eulota, Fruticicola, Euparypha, 

 Xerophila, including many sections and a vast number of species, 



*v. Ihering holds, I believe cnirectly, that the so-called darts of Zonitidffi are 

 not homologous with those of these Helices. 

 »See Pilsbry, Journ. de Conchyl., 1891, p. 22. 



