LYMNZZIDZ OF NORTH AMERICA. 379 
surrounding this species. It is closely related to catascopium, but is 
apparently distinct. It differs from catascopium in the form of the 
spire which is very acute, in the body whorl which is usually more 
globose and in. the columella which is not so sharply plicated. The 
aperture is also rounder than is that of catascopium. It is distinguished 
from palustris by its smaller size, lighter color, more broadly conic and 
shorter spire, more solid shell and lack of a distinct twist in the 
columella. These are minor differences, perhaps, but they are ap- 

Distribution of 
PALLIDA 
Geological 
Distribution 
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parently sufficient to distinguish pallida from palustris. The latter 
species occurs with pallida but is always darker in color and double 
the size when adult, besides being generally more fragile. 
Pallida has been quoted from California, Michigan, Iowa, Illinois 
and other western states; many of these references have been found 
upon examination of the specimens, to have been based on forms of 
obrussa (desidiosa authors). The statement of Adams that the sur- 
face is “without revolving striz’” has misled many conchologists to 
hunt for a smooth shell like humilis. Adams evidently meant that the 
