22 



LAND AND FRESH- WATER SHELLS OF N. A. PART III. 



is easily clistinguislied by having six wliirls, wliicli are mucli narrower 

 •than in that species. The spire is also almost double the length of that 

 of suhpurpurea, and the epidermis of a lighter color. (^Tryon.) 



Fig. 38. 



Operculum horny, rounded ; nucleus 

 subcentral ; lines of accretion concen- 

 tric. 



Operculum of V. subpurpurea. 



The lingual dentition of V. suhpurpurea is shown in Fig. 39. 



Fig. 39. 



Lingual deutitiou of Vivipara stthpurpurea. (Stimpson.) 



Fig. 40. 



Tivipara multicariiiata, Hald. — Shell conic, thin, subdiapha- 

 nous, green, whirls 5, longitudinally striate and 

 transversely carinate. 



This Paludina is thinner and lighter than our 

 species, and lias but 5 whirls. The length is about 

 one-fifth more than that of the last whirl, of which 

 the diameter is about double that of the j)enultimate 

 whirl ; beside the longitudinal strije, there are four 

 carinas, of which the first and third are stronger than 

 the second and fourth, and which cover the whole 

 length of eacli of the whirls. 



The opening is almost circular, yet the vertical is 

 greater than the transverse diameter. The lip is 

 slightly thickened, not acute ; the columella, which 

 is hardly distinct from the lip, joins the superior 

 termination of the aperture under a slightly acute angle. 



Palvdina carinata. 



