256 



JVes^ : PJiytophnikton of Englis/i Lake District. 



lakes. Careful measurements and drawings from September 

 1907 to August igoS showed that no seasonal form-variation 

 of this organism occurred in Windermere for at an}^ rate the 

 twelve months it was under observation, although Wesenberg- 

 Lund* has recorded such variations in the lakes of Denmark. 



The only other species of this group was Peridinium Willei, 

 and the collections showed the same sudden rise in the summer 

 months and gradual decline in the autumn as was exhibited b}^ 

 Ceratium hirimdineJla, the maximum being attained in August. 

 In two Italian lakes (Lago di Varano and Lago di Monate) this 

 species has been found b}' Lemmermannf to be a perennial 

 constituent of the plankton. 



Flagei.lata. Mallomojias longiseta appears first in October, 

 and as the temperature diminishes, its activity increases. It 

 reaches its greatest abundance in December (temp. 3.2° C.) 

 and then rapidly dies down, completely disappearing in March. 

 It thus appears to be a cold water type, thriving during the 

 autumnal fall in temperature. 



Dinohryon cylindriciim var. divergens has a considerable 

 maximum in September, in which month the temperature of 

 the water is the highest (14.4° C). This same variety occurred 

 in ver\' large quantity in Derwent Water in the month of June 

 1903. Lemmermann has also observed it more especially in 

 the warm period, and quite recently it has been found to attain 

 its maximum in the hot months in an Australian lake. J 



IV.— SYSTEMATIC ACCOUNT OF THE MORE NOTE- 

 WORTHY SPECIES. 



Among the various constituents of the phytoplankton of 

 the English lakes, a number of species are of sufficient interest 

 to merit special mention. Of the following 28 species, one is 

 here described for the first time (Dinohryon crenulatum), one 

 is new to Britain (Elakatothrix gelatinosa), and 13 are new^ to 

 England. 



CHLOROPHYCE.E. 

 I. BiNUCLEARiA TATRAXA Wittr. in Wittr. & Nordst. 

 Alg. Exsic. 1886, No. 715 ; fasc. 21, 1889, p. 18 (c fig.) ; G. S. 

 W^est, Treatise Brit. Freshw. Alg. 1904, p. 80, fig. 25. 



* Wesenberg-Lund, I.e.. 1908, p. 69. 



t Lemmermann in ' Archiv. fiir. Hydrobiol. n. Planktonkunde,' III., 

 1908, pp. 357, 361. 



i G. S. West in ' Jonrn. Linn. Soc. Bot.", XXXIX., 1909, pp. 17, 18. 



Naturalist, 



