190 



Mr. W. West and Dr. G. S. West. 



[Oct. 30, 



be added, such as sundry species of Chodatclla, Lagerheimia, Golenkinia, and 

 other genera. 



The following summary is instructive : — 



Totals of species for each 

 area, and grand total of 

 botli species and varieties 

 for entire British phyto- 

 plankton 



354 



Species only. 



Chlorophycese (except Des- 54 1 31 

 midiaceoe) 



Desmidiaceee ' 176 i 85 



Heterokontae j 5 — 



Bacillarieas 63 37 



Myxophycea? ' 31 17 



Phseophycese 1 2 | — 



Flagellata (except Peridi- 12 4 

 niece) 



Peridiniese 11 4 



178 



2 



Sh3 



Totals. 

 Species and varieties 

 of each group. 



Species. 



37 



103 

 2 

 47 

 33 

 1 

 13 



10 



246 



20 



101 



18 

 12 



6 



5 



24 



41 

 17 



4 



6 



33 



22 

 3 

 41 

 21 



3 



5 



81 



236 

 7 

 94 

 53 

 2 

 18 



15 



Varieties. 



18 



68 

 



22 

 2 

 

 7 



162 



188 



128 



506 



118 



G-rand total. 



The grand total of 506 species and 118 varieties is sufficient evidence in 

 itself that the British phytoplankton is exceedingly rich, and of this total 

 46 per cent, are species of the Desmidiaceee. 



Many of these constituents are, of course, adventitious or casual, consisting 

 of littoral or bog species which are carried into the plankton by the rains 

 and exist there only a short time before perishing. There are, however, 

 many constituents which are exclusively limnetic in , habit, and also others 

 which are much more abundant in the plankton than in other situations. 

 These have been discriminated in the foregoing list. 



XI. General Summary and Discussion on the Dominance of Desmids. 



The tabulated list gives a very adequate idea of the Algal constituents of 

 the British freshwater plankton, and also shows that many of these con- 

 stituents are common to the four British lake-areas. 



The British lakes combine to some extent the characteristic features of the 

 Central European and Northern European lakes, but are on the whole more 



