108 HELICID^. 



wliorls five, with delicate raised, oblique striae ; aperture 

 rounded, upright, its plane making an acute angle with 

 the axis of the shell, somewhat contracted by the lip ; lip 

 white, reflected ; base rounded ; umbilicus nearly cov- 

 ered by the reflected Up. 



Greatest transverse diameter five-eighths of an inch ; 

 ordinary size about half an inch. 



Geographical Distribution. Occurs plentifully in 

 the Western and Southwestern States, and in the States 

 bordermg upon Lake Erie. It has not hitherto been 

 noticed in the Eastern States. 



Remarks. This is a weU marked and beautiful spe- 

 cies. Its form is quite globular, especially in small indi- 

 viduals. Its surface is shining, and its strise of increase 

 deUcate and regular. Its aperture is rounded and the lip 

 reflected but not flattened. The umbilicus in specimens 

 entirely mature is covered, but, as commonly seen, a 

 small opening still remains. Its extreme diameter never 

 exceeds three-fourths of an inch, and sometimes does not 

 attain half that size. In the larger sijecimens the spire 

 is less elevated in proportion to the other dimensions. 

 The whorls are well rounded and do not exceed five. It 

 may be confounded with small specimens of H. pennsyl- 

 vanica, and of M. thyroidus in their immature condition, 

 but the former can be detected by its sub-triangular 

 aperture, and the latter, when closely examined, by the 

 rudiments of the tooth, exhibited by a slight thickening 

 in its place, resembling the touch of a pencil of varnish, 



