Sterki: North American Sph.eriid.e. 473 



Cyrenastrum Bourguignat, type S. solidum Xormand, of Europe; 



and including Nos. 1-30 of this Catalog; 

 CoRNEOLA Clessin, type S. corncum (Linne). Xos. 34-37, and probably 

 Nos. 31-33 of the foregoing Catalog. 



Genus Musculium. 



This is a well-defined genus, although the principal distinguishing 

 features cited by authors (high, "tubular" beaks, calyculate) do not 

 hold good. Subgenera cannot be defined, but there are about three 

 more or less well-marked groups. 



Genus PisiDlUM. 



Various attempts have been made to divide the Pisidia into sub- 

 genera or sections. Some of the divisions proposed are too artificial, 

 founded on arbitrarily chosen and partly mistaken features. Some 

 of the proposed groups have been too narrowly defined, or, on the 

 other hand, based upon too sweeping generalizations. Clessin's 

 groups Fluminina, Rivulina, and Fossarina suffer from these defects, 

 nevertheless appear to point out a natural arrangement. Accepting 

 Clessin's arrangement with some changes and additions, the sub- 

 joined grouping is tentatively proposed. Fontinalina may again 

 require modification. More detailed definition and discussion will 

 be found elsewhere. 

 Fluminina Clessin, type P. am?iicnm (Miiller), and P. virginiciim 



(Gmelin). This is a natural group, although the main distinguishing 



feature relied upon by its author proved to be based upon a mistake, 



the right valve having only one cardinal tooth, and not two teeth, 



as he supposed. 

 Lacustrina Sterki, type P. idahoense Roper. 

 RivuLlNA (Clessin) Sterki, type P. supiniim A. Schmidt, of Europe. 



Clessin included P. conipressurn Prime. Nos. 5-28, inclusive, of 



the foregoing catalog plainly fall into this division, and also Nos. 



29-33 (or 37) ; possibly also Nos. 38-40, inclusive. 

 Fontinalina Sterki, type P . fontinale Pfeiffer (-f- ahditum Haldeman). 



To this group belong many related palearctic Pisidia, and our Nos. 



41-85, and apparently also Nos. 86-101. 

 Fossarina Clessin (restricted), type P. ohtusaJe Pfeiffer, our Nos. 



102-111, characterized by a slight, short hinge, with very abrupt, 



