542 



MOLLUSCA 





Fig. 841 Fig. 842 



Fig. 841^BytMnia 

 tentaculata (Baker). 

 Fig. 842 Amnicola 

 limosa (Baker). 



B. tentaculata (L.) (Fig. 841). Shell yellowish or greenish in color, 

 smooth and shining, with 5 whorls, the lowest of which equals the other 

 four; length 11 mm.; width 6.5 mm.: a European species introduced 

 recently into the northern states; in lakes and ponds, often very 

 common; in Chicago they are sometimes drawn into 

 the water pipes from Lake Michigan in sufficient 

 quantities to block the smaller ones. 



2. AMNICOLA Gould and Haldeman. Shell small, 

 thin, smooth, conical, with a low spire and a broad 

 lower whorl; operculum spiral, horny; snout short, 

 tentacles long: about 10 species, all in North Amer- 

 ica, in fresh water; 3 on the Pacific slope. 



A. limosa (Say) (Fig. 842). Shell globose, plain 

 brown in color, without bands, shining, 5 mm. long, 

 4 mm. wide ; umbilicus either narrow or wide ; whorls 



4 to 5 ; aperture circular ; lip sharp : entire country ; very common on the 

 muddy bottom or on aquatic plants in streams and ponds. 



A. cincinnatiensis (Lea). Shell swollen, greenish or yellowish- 

 brown in color, smooth and shining, 5.5 mm. long, 4 mm. wide; whorls 



5 or 6; aperture oval; lip sharp; umbilicus small and very deep: eastern 

 and central states ; common on the muddy bottom of streams and ponds. 



3. FLTJMINICOLA Stimpson. Shell rather large, ovate, solid, without 

 umbilicus, smooth, outer lip projecting above over the inner lip, which 

 is flattened: Pacific slope, in streams and lakes. 



F. nuttalliana (Lea). Shell yellowish, smooth, with 4 whorls; 

 aperture white; length 10 mm.; diameter 7.5 mm.: valley of the 

 Columbia; very common. 



4. SOMATOGYRTIS Gill. Shell globose, with a short low 

 spire and a very large inflated lower whorl and large 

 oblique aperture; whorls 4; lip thin; operculum spiral, 

 horny: about 6 species, all in the central states, in fresh 

 water. 



5. subglobosus (Say) (Fig. 843). Shell yellowish in 

 color, shining; apex rounded; length 7 mm.; width 6.5 

 mm.; umbilicus small: central states, west to Iowa. 



S. integer (Say). Shell yellowish, shining, 4 mm. long and 3 mm. 

 wide; umbilicus almost obliterated by a callus: central states, west to 

 Iowa. 



5. POMATIOPSIS Tryon. Shell small, elongate, and conical; umbili- 

 cus narrow and deep; aperture round or oval; operculum spiral and 

 corneous; peristome thin: North America; air breathers,, although 

 possessed of a gill. 



Fig. 843 



Somatoyyrus 



subglobosus 



(Baker). 



