1888.] PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 369 



A STUDY OF THE AMERICAN SPECIES OF VERTIGO CONTAINED 

 IN THE U. S. NATIONAL MUSEUM, WITH THE DESCRIPTION OF 

 A NEW SUBGENUS OF PUPID/E. 



BY V. STERKI, M. D., OF NEW PHILADELPHIA, OHIO. 



(With Plate xlii. i 



The North American forms of Pupa are far from being well known : 

 this is especially the case with those belonging to the genus Vertigo. 

 Though among the most interesting of all our mollusca, the shells of 

 this section of the Pupidw seem to be the most neglected. This may be 

 clue to two causes : First, their minute size and the supposed or real 

 difficulty in collecting them ; and, second, their apparent similarity and 

 the critical skill required to separate and determine them. The multi- 

 tude of features and the possibilities of their combination are greater 

 than generally realized, but since many of their characteristics are 

 rather constant, it is not so difficult to separate and define the different 

 species as appears at first. Once become familiar with these little creat- 

 ures and the observer will find them far more manageable than many 

 a group with much larger shells, just as a botanist at first dreads the 

 determining of Cyperacew, and when versed in them likes them better 

 than any others. 



The Vertigos are particularly interesting because of their close rela- 

 tionship to Europeau species. When the American species have been 

 as thoroughly studied and are as well known as those of the Old World, 

 it will probably be found that they form part of the great circumboreal 

 laud-shell fauna — like other groups of the mollusca that are distributed 

 through the north temperate zone in the contiguous continents. They 

 exhibit analogous features of resemblance and vary perhaps not in so 

 extreme a degree as the Limnceas, but as much as other members of the 

 fauna as a whole, aside from the Protozoa. For this reason it would be 

 worth while for collectors to obtain as many specimens as they can, since 

 not only new species will doubtless be detected, but with an abundance 

 of material it will be possible to study their variations throughout the 

 continent, and last, but not least, their geographical distribution, and 

 enable us to make a comparison of the same with that of the Old World. 

 For some time past I have been studying our Vertigos as far as I could 

 obtain specimens from different States, and have compared them with 

 European forms. The results obtained appear to me interesting enough 

 to be published, at least in part. Considering the few species thus far 

 described the results are not definite, and I have been careful to make no 

 conclusions beyond such as follow directly from the examination of the 

 material in hand. This has been for the most part only the shells ; as 

 ProcN. M. 88—24 ^^SV*^- 



