They are inhabitants of fresh water, chiefly in the tro^ 

 pical regions ; but many species are very abundant in the 

 rivers, lakes and small streams of the United States. No 

 recent ones have been found in Europe, but several have 

 occurred fossil in comparatively recent formations. No 

 fossil species have yet been found in this country. La- 

 marck described sixteen recent and twelve fossil species ; 

 but Defrance enumerates thirty-six species. 



MELANIA NUPERA. 



SPECIFIC CHARACTER. 



From one to four or more revolving series of tubercles. 



DESCRIPTION. 



Shell oblong suboval : volulions five, slightly rounded : 

 body whorl with about three revolving series of subequal, 

 equidistant, granules or tubercules, not higher than wide, 

 occupying the superior portion of the surface ; secmid vo- 

 lutmi with but two series ; remaining volutions with 

 slightly elevated, longitudinal lines instead of tubercles, 

 often obsolete : spire decorticated towards the tip : sidiire 

 not deeply impressed : aperture longer or as long as the 

 spire ; sinus of the superior angle profound : labium con- 

 cave, with a callus near the superior angle : columella with 

 a slight, obtuse, hardly prominent angle above the incipi- 

 ent sinus, which is obvious : labrum not abbreviated above, 

 nor much produced near the base. 



PLATE VIII. 



