144 HELICID^. 



lip Tvliite, narrow, reflected, with a deep groove or inden- 

 tation behind the reflection, contracting the opening so 

 that the outer edge of the lip does not project beyond 

 the surface of the whorl ; on tlie inner margin of the lip 

 are two acute teeth, with the points directed inwards, 

 one near the base, the other midway between that and 

 the junction of the lip with the body-whorl, with a circu- 

 lar sinus between them, forming one of the lobes of the 

 aperture ; pillar-lip with a long, arcuated, white tooth ; 

 umbilicus covered, its place considerably impressed. 



Greatest transverse diameter, one half of an inch ; 

 ordinary size, about one-third of an inch. 



Geographical Distribution. Inhabits the Western 

 States, on the borders of the Ohio and Mississippi 

 Elvers ; it was noticed by Mr. Say in Missouri, and by 

 others m North Carolina, Tennessee, Arkansas, and 

 Michigan. It has not been observed upon the Atlantic 

 ooast. 



Remarks. This species is not likely to be mistaken 

 for any other. It resembles that variety of Helix tri- 

 dentata called by Mr. Say Helix fallax ; but it differs 

 from it in having the umbihcus entirely covered. The 

 resemblances of the two are in some instances so striking 

 as to suggest the thought, that the greater development 

 of the lip at its junction with the base of the shell may 

 be only an accidental circumstance, due to locality or 

 some other cause ; and that the two may be only varieties. 

 The umbilicus, in those species which possess it, is so 



