230 



great seasonal polymorphism in B. cornuta near Basel. Zacharias 

 ('97a and '98b) records it in the plankton of German carp ponds. 



Stenroos ('97 and '98) finds it in waters of Finland and Karelia, 

 where the cornuta type is littoral, and a limnetic form, distinguished 

 by him as forma vernalis, is abundant in the plankton in May. Scour- 

 field ('98) finds it common in the waters of Epping Forest, where it 

 is perennial, males and ephippia appearing only in September- 

 November. According to Scott ('99) it appears at various seasons 

 in the lochs of Scotland in both the littoral and limnetic fauna. 

 Burckhardt ( 'OOa) gives an extensive revision of the genus Bosmina, 

 and includes in the B. longirostris group nine other so-called species, 

 among which are B. cornuta Jur. The species is "pelagic or hemi- 

 pelagic" in various Swiss lakes, though apparently not in num- 

 bers. The genus is there represented in the plankton princi- 

 pally by the B. coregoni group. Amberg ( '00) lists it from Katzen- 

 see, near Zurich, as a perennial planktont with large numbers in 

 May, August, and February, but gives no statistical data. Fuhr- 

 mann ('00) finds Bosmina perennial in Neuenburgersee, and B. 

 longirostris with a maximum in May. Marsson ('00) finds B. 

 " longirostris-cornuta " in lakes about Berlin throughout the year, 

 with larger numbers in some lakes during the warmer months and 

 in others in November-December. In Barlewitzersee, near Danzig, 

 Seligo ('00) reports B. cornuta as perennial, with maxima in June 

 and in October-November, the latter being the greater. Larger 

 numbers appear in summer than in winter. Cohn ('03), in waters 

 near Konigsberg, finds B. longirostris only sparingly present, 

 appearing in May-September with a maximum in July. 



In European streams, also, B. longirostris is widely distributed. 

 Lauterborn ( '94) finds it abundant in the winter fauna of the Rhine. 

 He also states that it is not acyclic in the backwaters, where he has 

 found in three successive years both males and ephippia in May- June 

 and again in November. There is thus a suggestion of a vernal and 

 an autumnal pulse in these waters. Zimmer ( '99) finds it through- 

 out the whole year in the Oder. Schorler ( '00) reports it from the 

 Elbe at Dresden in May-October, with larger numbers in May- June 

 and September, while Fric and Vavra ('01) find it in the same 

 stream near Podiebrad. They state that B. cornuta is found in 

 great numbers in 1 m.- surf ace in summer months, and B. longiros- 

 tris sparingly in the littoral fauna. Steuer ('01) finds B, ' 'longirostris- 



