167 



Ampularia, and Valvata, and from these, in addition to other 

 differential traits it may be distinguished by the disunion above of 

 the labia). It strongly resembles Melanopsis, Pirena and Potam- 

 ides, but these are distinctly and unequivocally emarginated at 

 base. 



The animal respires water j it has a short, conic-cylindric, obtuse 

 rostrum; two acute tentacula having the eyes at their exterior base ; 

 foot short and obtuse. 



They are inhabitants of fresh water, chiefly in the tropical re- 

 gions ; 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. Lamarck described sixteen recent and twelve fossil spe- 

 cies ; but Defrance enumerates thirty-six species. 



Melania nupera,* — Specific character. From one to four or 

 more revolving series of tubercles. 



Ohs. It varies in the number of its series of tubercles, some 

 specimens having but one, and others, though these are rare, as 

 many as five or six. Plate 8. Middle figure exhibits the young 

 shell. 



Melania depygis.* — Specific character. Body whorl yellow- 

 ish, with two equidistant, revolving, rufous lines. 



Ohs. It varies a little in color, and a few occurred, of which 

 the color is fuscous, the bands being obsolete: PI. 8, lower figures. 



Lutraria. — Shell equivalve, inasquilateral, transversely oblong 

 or subovate, gaping at the extremities, particularly at the posterior 

 extremity ; cardinal teeth two, of which one is doubled in the 

 shape of a V, the other simple, with a large deltoid cavity situated 

 obliquely near the teeth ; lateral teeth none ; ligament internal, in- 

 serted in the cardinal cavities, not visible when the shell is closed ; 

 mascular impressions two, lateral, remote, simple ; impression of 

 the mantle extending to the muscular impressions and having a 

 large and profound sinus extending nearly half its length. 



Obs. Lamarck separated this group from the Linnaean Mactrse, 

 from which it is essentially distinct by the absence of lateral teeth 



* [Mr. Say makes no reference to the previous descriptions of this spe- 

 cies in N. H. Diss. — Ed.] 



