Fig. 20. 



26 LAND AND FRESH- WATER SHELLS OP N. A. [PART I. 



The niidclle tooth of the lingual ribbon short, tricuspid ; 

 laterals of the same shape, but bicuspid ; uncini thorn-shaped, 

 curved. 



TITRIIVA, Drap. 



Shell imperforate, pellucid, glassy, depressed ; spire short ; 

 whirls 2-3, rapidly increasing, the last dilated ; aperture ample, 

 peristome thin, often membranous. 



Animal : body elongated, limaciform ; 

 mantle covering the back and neck, and 

 extending to the base of the eye- 

 peduncles, with one or more processes- 

 or prolongations of its margin, which 

 are reflected upon the shell ; tentacles very short. Respiratory 

 orifice in the mantle, behind its usual position in the 

 Limaces. Generative orifice behind and below the 

 eye-peduncle. 



Jaw arcuate, concave margin with a median, beak- 

 like projection. 

 Lingual membrane with long slender teeth ; centrals tricuspid, 

 laterals bicuspid, in straight transverse series ; uncini long, 



Animal of Vitrina.^ 



Fig. 21. 



Fig. 22. 



Lingual dentition of V. limpvia. [Morse.] 



curved, thorn-shaped, bidentate, in a curved transverse series, 

 and diminishing in size as they pass off laterally. 



Titrina limpida, Gould. —Shell globose-discoid, thin, fragile, 

 transparent, shining ; whirls two and a half to three, scarcely convex, with 

 very minute lines of increase, the last whirl large, and much expanded ; 



' V. major from Moi^uin-Tandon. 



