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* Gnathophora. 

 Mouth armed with a jaw. Mostly phytophagous. 



) Holognatha. Jaw simple, without superior appendage. 

 Yitrini, Helices, Bulimi, Cylindrellse, Pupae, Limaces, etc. 



f f Elasmognatha. Jaw with a superior quadrangular acces- 

 sory plate. Succinefle. 



j" Holognatha. 



FAMILY VITEINID^E. 



Animal with or without a caudal mucous pore, the tail some- 

 times obliquely truncate ; mantle-margin sometimes more or less 

 reflexed over the sides, or entirely covering the shell, which the 

 animal is frequently too large to entirely enter, locomotive disk 

 longitudinally tripartite. 



Jaw not ribbed, with a median inferior projection. 



Shell usually thin, corneous, transparent, normally spiral, of 

 few, rapidly enlarging whorls ; sometimes a plate, with or without 

 spiral nucleus. 



Synopsis of Genera. 



* Without caudal mucous pore. 

 Genus YITRINA, Draparnaud, 1801. 



Shell imperforate or very narrowly perforate, depressed or 

 subglobose, very thin, corneous, pellucid ; spire small, whorls 

 few, rapidly increasing, the last large ; aperture large, lunate or 

 rounded, the colurnellar margin slightly inflected, peristome 

 often membranaceous. Animal (PI. 29, fig. 3), proportionally to 

 the shell, large, not able to withdraw into its shell, or entering it 

 with difficulty ; body elongated, tail short, without mucous pore ; 

 mantle covering a part of the neck, reflected over the margin of 

 the shell, and furnished with a spatulate posterior lobe on the 

 right side, continually moving over the surface of the shell, 

 which it polishes. Jaw (PI. 29, fig. 1) with an inferior rostriform 

 projection. The central tooth of the lingual ribbon is tricuspid, 

 the laterals, and the thin acuminated marginals, bicuspid (PI. 29, 

 fig- 2). 



Yitrinas live in moist situations, among loose earth, stones, 



