- inhabiting the United States. 357 
Greatest transverse — less than three-fourths 
of an inch. 
Grocrarmicar Disrriurion.. Inhabits all the 
Western and Southwestern States. ; 
Remarks. I consider this species not to be well 
established. The’ description of. Mr. Say hardly 
points out any difference between it and the preced- 
ing, and accordingly varieties of H. pallidta are com- 
monly seen in cabinets labelled as H. appréssa. Well 
marked specimens of the two are very unlike, but 
they approaeh each other by nice and hardly appre- 
ciable shades of difference, until they at length seem 
to blend into one. It is impossible to say how far 
the charaeters of shells are modified by th: ccident 
of their locality and other causes; but that they are 
so to a considerable degree is certain, and it appears to 
me that the differences between this and the preced- 
ing species, are not greater than might be. produced 
by the influence of external circumstances. "The 
shell intended to be described is very common in the 
Western and Southwestern States, is usually only 
about half as large as H. palliàta, and considerably 
more flattened in shape. It has a smooth and shining 
epidermis; without the hirsute projections, and is fine- 
ly striated. The lip is narrower and less broadly 
expanded, the aperture much less contracted, and the 
tooth on the pillar-lip less prominent and thick than 
in that species. The teeth on the outer lip are some- 
times entirely wanting, at other times very distinct; 
sometimes the upper.and sometimes the lower one is 
alone present. The smaller sized specimens resem- 
ble considerably Hxrix inflecta, Sav, and it seems 
