North American Terrestrial Mollusks. 163 



the jaw, or on the presence or absence of striae or ribs on its 

 anterior surface, at least as subfamil}'^ characters. We have 

 recognized, therefore, at present three forms of jaw only, 

 viz. : 1st, simply in one piece ; 2cl, in one piece, with an 

 upper accessory plate ; 3d, in numerous separate, free, im- 

 bricated pieces. Some modifications even in these distinc- 

 tions will, we believe, soon prove necessary, as several forms 

 of accessory plate have already been noticed,* and the jaw 

 of Punctum, figured by us on p. 222, is a modification of 

 that of Orthalicus figured on p. 215. 



We admit two distinctions on the lingual membrane for 

 the purpose of grouping the genera into subfamilies, viz. : 

 marginal teeth conical, separate, aculeate ; and marginal 

 teeth crowded, quadrate, dentate or serrate. 



Based upon these characters we propose the following 

 grouping of the North American genera of HelicidoB:^ 



ViTRiNiN^. Jaw in one piece. Marginal teeth separate, 

 conical, aculeate. — Macrocyclis, Zonites, Hyalina, Vitrina, 

 Limax. 



Helicin^. Jaw in one piece. Marginal teeth crowded, 

 quadrate, dentate or serrate. — Arion, Ariolimax, Binneia, 

 Patula, Helix, Holospira, Cylindrelhi, Macroceramus, Buli- 

 mulus, Cionella, Stenogyra, Pupa, Vertigo. 



Orthalicin^. Jaw composite, in numerous, free, im- 

 bricated pieces. Marginal teeth crowded, quadrate, dentate 

 or serrate. — Orthalicus, Liguus, Punctum. 



SucciNiN^. Jaw in one piece, Avith one upper accessory 

 plate. Marginal teeth crowded, quadrate, dentate or serrate. 

 — Succinea. 



Subfamily ViTRiNiN^. (p. 25). — The following description 

 is to be substituted for that oriven : 



Jaw in one piece, smooth, usually striated, never I'ibbed, 



* See Eucalodium, Joiirn. de Conch., 1870, pi. v, flg. 1. 



t Gill, in fact, embraces in his section Soloynatha, all the genera included in our suh- 

 families Vitrinince and Helicinoi with tlie exception of JinUmulufi, regarding which he 

 adopts the views of Albers and von Martens, placing it in tlie section Gotnognatha, with 

 Orthalicus. (Arrangement of the Families of Mollusks, Washington, 1871.) 



