Wes^ : Phytoplankion of English Lake District. 327 



the Desmidiaceae. In some of the lakes Desmids are abundant, 

 but they rarely occur in such prodigious quantities as certain 

 species of Diatoms and Flagellates, although the May plankton 

 of Ennerdale Water, and also of Easedale Tarn, was for the 

 most part a Desmid plankton. Notwithstanding the fact that 

 the English Lakes contain a high percentage of species, taken 

 generally, they are not so rich in actual numbers of Desmids as 

 the Scottish or Welsh lakes. The most frequent Desmids are : 

 Staurastrum anatinum, St. Arctiscon, St. curvafum, St. jaculi- 

 ferum, St. lunatum var. planctonicum, C. suhtumidum var. 

 Klebsii, Xanthidium antilopceum and vars., Arthrodesmus 

 Incus, A. triangularis, and Spondylosium pidchrum var. planum. 

 In the plankton of some of the lakes, and especially in that of 

 Brothers' Water, St. Arctiscon is abundant. 



Staurastrum sexangulare was present in the plankton of 

 Ennerdale Water, and St. Ophiura in Easedale Tarn. 



St. Ophiura is a feature of the plankton of many of the 

 Scottish,* Welsh, and Scandinavian lakes ;f and its occurrence 

 in the plankton of Easedale Tarn is very interesting. 



Until British plankton-investigations were started about 

 eight years ago, both St. Arctison and St. Ophiura were regarded 

 as amongst the rarest of British Desmids. It is now known 

 that both occur in myriads in the plankton of certain lakes, 

 whereas they are very rarely found in the surrounding bogs, 

 or even at the boggy margins of the lakes in which they occur. 

 The occurrence of Micrasterias pinnatifida, M. radiata, and 

 M. mahahidcshwarensis var. Wallichii is also of great interest 

 in comparison with the plankton of the other British lake-areas. 



The general abundance of Spondylosium pulchrum var. 

 planum deserves special emphasis. It also occurs abundantly 

 in the Scottish and Irish lakes. Bachmann has recorded the 

 occurrence of ' Spondylosium pulchrum ' in several Scottish 

 lochs, J but in this he is wrong. Typical Spondylosium pul- 

 chrum does not occur in the British Islands, but Wolle's var. 

 planum, which is much smaller, more regular, and without any 

 twist in the filaments, is quite common in the British plankton. 



* W. & G. S. West in ' Journ. Linn. Soc. Bot.', XXXV., Nov. 1903, 

 pp. 530 and 550 ; in ' Trans. Roy. Soc. Edin.', XLI., 1905, p. 487. 



f Lemmermann, ' Das Plankton Scliwedischer Gewasser,' Arkiv. for 

 Botanik iitgifv. af K. Sv. Vet.-Akad. Bd. 2, No. 2, 1904 ; Huitfeldt-Kaas, 

 ' Planktonundersogelser,' I., Norske Vande, Christiania, 1906. 



I Bachmann, loc cit., 1907, pp. 21, 26, 27, 30, 88. 



1909 Sep. 1. 



