HELIX. Ill 



cated, aperture oblique, more or less trilobed, the peristome callous, 

 insinuated or dentate. H. OBVOLUTA, Mull. 



Europe. 



Helicodonta, Risso, 1826, Vortex, Beck, 1837, and Euphemia, 

 Leach (teste Beck), 1844, are synonyms. 



.Subsection III. CARACOLINA, Ehrenb, 1831. 



Shell depressed, lenticular, the periphery obtusely angulated to 

 acutely carinated, aperture narrow, oblique, somewhat basal, with 

 or without teeth on the lip. H. LENS, Fer. 



Europe. 



Section II. POLYGYRA, Say, 1817. 



Widely or moderately umbilicated, orbicular-planate, usually 

 obliquely costulate-striate ; whorls slowly increasing, the last con- 

 stricted behind the aperture, shortly descending ; aperture subreni- 

 form or irregularly sinuated, peristome narrowly reflected, callous, 

 sometimes dentate within, the parietal wall often with a triangular 

 callus, connecting with the peristome, and more or less tooth-like. 

 H. AURICULATA, Say. 



United States. 



Subsection I. POLYGYRATIA. Gray, 1847. 



Shell discoidal, plane above, concave below; whorls numerous, 

 narrow, all equally visible above and below, the last descending in 

 front ; aperture oblique, Innately rounded, the peristome margined, 

 shortly reflected, interior unarmed. H. POLYGYRATA, Born. 



So. America. 



Ophiogyra, Albers (in part), 1850, Systrophia, Pfr., 1855, and 

 Mierophyura, Ancey, are synonyms. 



:Subsection II, POLYGYRA, Say (sensu stricto). 



Widely umbilicated, planorboid, many whorled, whorls narrow, 

 ribbed above, periphery angulate ; aperture small, trigonal, with a 

 Y-shaped parietal tooth, joining the lip-extremities. H. CEREOLUS, 

 .Muhlf. 



So. U. S. and West Indies. 



Subsection III. POLYGYRELLA, Bland, 1869. 



Widely umbilicated, discoidal, ribbed above ; whorls 7-8, nar- 

 row, the last deflected at the aperture ; aperture subvertical, the 

 margins joined by a parietal triangular tooth, interior with two 



