582 UNITED STATES GEOLOGICAL SURVEY OF THE TERRITORIES. 



Limnw, Montf. (1810), Couch. Syst., II, 262. 



Omphalia, Raf. (1819), Jour. Phys., LXXXVIII. 423. 



Limnula, Raf. (1819), i&. 



Gulnaria, Leach, MS. (1820, Syn. Brit. Moll., I4(i).— Turton (1831), Man., 117.— Hartni. (1840), 



Syst. Uebers. ; ami ( 1H44) Erd- nud Siissw. Gast., I, 63. 

 Stagnicola, Leacli, MS. (1820, Syn. Brit. Moll., 112).— Gray (1840), Turlou's Mau. (2ded.), 239 



(as a subgenus under Limnwa). — Beck (1846), vid. Amtl. Ber. Vers, in Kiel, 123 (as a 



subgenus under Limnaa). 

 Limnophysa, Fitzinger (1833), Syst. Verz , 112.— Beck (1837), Iud., 110 (as a subgenus under 



Limnaa). — H. and A. Adams (1855), Genera Recent Moll., 11,254 (as a subgenus under 



Limnwa). 

 Leptolimnea, Swainson (1^40), Malae., 338 (as a subgenus under Limnwa). 

 Bulimnea., Haldeman (1842), Fresh-water Univalves U. S., 14 (as a subgenus uuder Limnaa).— 



H. and A. Adams (1855), Genera Recent Moll., II, 254 (as a subgenus under Limnwa). 

 Acella, Haldeman (1842), Fresh- water Univalves U. S. 14 (as a subgenus under Limnwa).— H. and 



A. Adams (1855), Genera Recent Moll., II, 255 (as a subgenus under Limnwa). 

 Pleiirolimnwa, Meek (1866), in Conrad's Smithsonian Check-List N. Am. Eocene Invert. Fossils, 



9 and 34. 



Etym. — ?.ifivaioc, marshy, or from the water. 

 Type. — Helix stagnalis, Linn. 



Shell dextral, subovate, or more or less elongated, horn-colored ; spire 

 acute, short, or variously produced ; volutions convex, last one most generally 

 ventricose, rarely all flattened ; aperture usually large, wide, nearly always 

 rounded anteriorly; outer lip simple; inner lip generally with an oblique 

 fold; surface very rarely with little ridges parallel to the lines of growth. 



The above diagnosis includes eight sections or subgenera, six of which 

 are adopted by II. and A. Adams and some other concbologists ; and two 

 others I have proposed for the reception of peculiar fossil species. These 

 groups may be severally distinguished as follows : 



1. limnaa, Lamarck (typical). 



Shell with spire more or less produced ; last whorl ventricose ; 

 fold of inner lip well developed — (Type as stated above.) 



2. radix, Mont Ibrt (rr Gulnaria, Leacli). 



Shell subovate; last whorl and aperture very large, the latter 

 being greatly expanded, and more than half the length of the shell. — 

 (Limncea auricularia, Linn.) 



3. polyrhytis, Meek. 



Much like the last in form, but bearing distinct, regular, vertical 

 costre. — (L. Kingi, Meek.) 



4. bulimnea, Haldeman. 



Shell thick; spire short; outer lip expanded. — (L. megasorua. 

 Say.) 



