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 

 CATASCOPIUM 



FIG. 44. 



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 striae" has misled many conchologists to 

 hunt for a smooth shell like humilis. Adams evidently meant that the 



