144 NATURAL HISTORY BULLETIN. 



quite as characteristic of the loess show similiar peculiar- 

 ities of distribution. Thus Pupa muscorum (L.)> widely 

 distributed in the loess of Iowa and Nebraska, is now 

 found living in this country only in the north, from Maine 

 to Montana, and thence through the dry western regions 

 to Utah and Nevada, and its near relative, Pupa blandi 

 (Morse) Binn., also frequent in the loess, is likewise 

 found only in the dry west, from the Dakotas to New 

 Mexico; Spliy radium edentulum alticola (Inger.) Pils., a 

 common loess fossil, while scarcely distinct from the type, 

 is the form commonly living in the Rocky Mountain 

 region, and occurs only sparingly with the type eastward; 

 Pyramidula strigosa iowensis Pils., the fossil form, while 

 now considered extinct, belongs to a species which now 

 spreads over all the western dry regions from Montana and 

 Washington to Mexico, and its extremely great variation 

 in form, size and sculpturing warrants the belief that the 

 now fossil form was a mere geographical race in no wise 

 outranking the dozen or more living varieties of Pyramid- 

 ula strigosa now recognized; while less marked examples 

 are found in such species as Vallonia gracilicosta Reinh., 

 Sucdnea grosvenorii L,ea and Helicina occulta Say, which, 

 though now living, are yet entirely extinct in many 

 localities in which the fossils are found. There is, 

 therefore, nothing unique in the relative distribution 

 of the recent and fossil shells herein discussed. 



That the first-described, and for many years only known, 

 specimens of this species were fossils is an interesting fact 

 which has its counterpart in the history of another common 

 loess fossil, Helicina occulta Say, which was described by 

 Say from fossil specimens, and which for many years was 

 regarded as extinct. Yet it has been discovered living in 

 widely-separated isolated colonies from Virginia and 

 Pennsylvania to Wisconsin and Iowa. 



It is interesting to note in this connection that the few 

 species of loess fossils which form marked exceptions to 



