34 HELICID^. 



sublabiate, reflected, its extremities approaching. 6 sp. E. Asia. 

 H. oculus, Pfr. 



POLYGYRA, Say, 181T. Shell planorboid, many-whorled, whorls 

 narrow, ribbed above, periphery angulate ; aperture small, 

 trigonal, with a V-shaped parietal tooth, joined by a raised callus 

 to the extremities of the lip, but no lip-teeth ; below plane, 

 showing several whorls, with a narrow umbilicus ; horn-color. 

 H. septemvolva, Say (xciv, 26, 2*7). 22 sp. Southern United 

 States, Mexico, West Indies, So. America. 



Dsedalochila^ Beck, 1837. Shell small, depressed, ribbed- 

 striate, periphery angulate, below convex, showing more than 

 one, sometimes two whorls, with a minute central perforation ; 

 lip auricular, with internal teeth, marked externally by scrobicu- 

 lations ; parietal wall with a Y-shaped tooth, callously joined to 

 the extremities of the lip. H. auriculata^ Say (xciv, 28, 29). 

 22 sp. Southern United States, Mexico, W. Indies, etc. 



Polygyrella, Bland. (Adelodonta, Ancey.) Shell discoidal, 

 ribbed above ; two rows of three teeth within the last whorl ; 

 peristome thickened, simple, margins joined by a pliciform 

 elevated triangular plate. H. polygyrella, 'Blsiiid (xciv, 30, 31). 

 Washington Terr., U. S. 



Avimonitella, Cooper. Each whorl largely enclosed by its 

 successor, so that the spire forms a crateriform depression ; 

 aperture vertically narrow ; peristome obtuse, thickened ; umbil- 

 icus large. A. Yatesii, Cooper (xciv, 32, 33). California. 



STENOTREMA, Raf., 1819. (Stcnostoma, Raf., 1831.) Shell small, 

 often hirsute ; aperture narrowly transverse, basal, extending 

 from the periphery to the axis of the shell ; parietal wall with a 

 long lamellar tooth, lip broad, with generally a notch in the 

 centre. Within the aperture, and near the axis, may be seen an 

 accessory column or pillar, probably assisting the animal in 

 retiring within its shell. H. hirsuta, Say (xciv, 34). 10 sp. 

 United States, mostly east of the Rocky Mountains. 



TRioDOPSis,Raf., 1819. Shell globosely depressed, umbilicate ; 

 aperture trilobate, caused by denticles on the superior and 

 inferior parts of the lip and on the parietal wall. H. tridentata^ 

 Say (xciv, 35). 8 sp. United States. 



Xolotrema, Raf., 1819. Shell turbinate or depressed, frequentl}^ 

 angulate or carinate on the periphery; base convex, imperforate; 

 aperture trigonal ; lip with a long lamellar tooth at the base, and 

 frequently a small superior tooth ; parietal wall with a large 

 curved lamellar parietal tooth. H. palliata, Say (xciv, 36). 3 sp. 

 United States. 



Isognomostoma, Fitz., 1833. (Helicodonta, Moquin-Tandon, 

 1855.) Shell small, globosel}^ depressed, umbilicus covered by 

 the extremity of the lip ; aperture tridentate, the two lip-teeth 

 small, the parietal tooth larger, blade-shaped. Horn-color, fre- 



