BITHINIA. 15 



generally more or less ventricose. The more produced 

 is the shell, the less convex are the turns. The suture 

 is distinct but fine, and the whorls, instead of jutting 

 out abruptly, as in Leachii, shelve gently downwards. 

 The general proportion of their breadth to their height 

 is as two to one. The apex is very small, and rather 

 pointed ; the enlargement of the succeeding volution is 

 sudden. There is no true umbilical cavity, but at most 

 a slight crevice behind the pillar-lip, which latter is 

 narrow, somewhat appressed, and not dilated anteriorly. 

 The aperture is snbpyriformly ovate or obovate, being 

 contracted to a point at its posterior extremity. It occu- 

 pies three-sevenths of the entire length of the shell, and 

 not half of the greatest breadth. The outer lip is some- 

 what disposed to expand, and is slightly thickened within 

 by a white ridge, which forms a support for the oper- 

 culum. Our largest specimen measures a third of an 

 inch in breadth, and rather more than half an inch in 

 length. 



Animal usually dusky, almost purplish-black, speckled 

 with brilliant yellow, sometimes of a general pale tawny 

 hue ; muzzle long ; tentacula dusky, slender, equal, scarcely 

 thickened at their bases, and bearing near their outer 

 bases small black eyes, on slight prominences. A single 

 small veil on the right side of the neck. Mantle lax, 

 but thickened at the edge. Foot oblongo-triangular, 

 rounded behind. Denticles of the tongue with numerous 

 very prominent linear marginal crenations. 



This species is found in ditches, canals, and slow small 

 streams throughout the greater part of England, appa- 

 rently becoming rarer in the north. It is doubtfully 

 recorded as an Aberdeenshire shell by Macgillivray, most 

 probably from ballast; we have taken species undoubt- 



