1908.] The British Freshwater Phytoplanhton. 



173 



well represented by species of Anabeena and Oscillatoria, the narrow limnetic 

 species of Lyngbya, species of Coelosphcerium, Gomphosphczrw.m, and Aphano- 

 thece: and Chroococcus Umneticus is abundant. Three species of Dinobryon are 

 fairly common, but we have no evidence to show whether they ever become 

 dominant or not. 



On the whole, the phytoplankton is a combination of that which occurs in 

 shallow lakes with that of large pools and ponds. Out of a total of 

 128 species observed in it, 17"! per cent, were Desmidiacea?, 25 - 7 per cent, 

 other Chlorophycese, 32 per cent. Bacillarieai, and 16"4 per cent. Myxophyceae. 



VI. The Welsh Lake-area. 



Plankton collections were made from 19 of the Welsh lakes, mostly those 

 of Carnarvonshire, during June, 1905, August and September, 1906, and 

 April, 1908* 



The phytoplankton of the spring and summer is essentially Chloro- 

 phyceous, and as in the case of the Scottish lakes, is especially noteworthy 

 for the abundance of its Desmids. There is little bulk even in the summer 

 plankton, and in general it has practically no effect on the colour of the 

 water. The Desmid-Jlora in certain of these lakes is equal to that found in the 

 richest kikes of the north-west of Scotland, ami in one case — the Capel Curig 

 Lakes — is superior to that known from any other lake in the world, which has 

 been biologically investigated. 



Of a total of 162 -species which we have observed in the phytoplankton 

 of the Welsh lakes no fewer than 101 are species of Desmids. 



The Protococcoideee are relatively few, both in number of species and 

 individuals, A akist'rodesmus falcatus and Botryococcus Braunii being the most 

 frequent. 



Diatoms are not conspicuous, and there are fewer species in the Welsh 

 plankton than in either the Scottish or Irish lakes. 



Apart from the spasmodic occurrence in fair quantity of one or two species 

 of Anabazna, and the moderate abundance of Oscillatoria Agardhii, the blue- 

 green element is distinctly scarce in the Welsh plankton. 



Species of Dinobryon and various Peridiniea? occur abundantly in the 

 Welsh lakes. Ceratium cornutum is more abundant than in any other part 

 of the British Islands. 



There is no great development of peat in this Welsh lake-area, and the 

 water of the lakes is for the most part clear and limpid. The drainage is 

 mostly down steep mountain sides, with occasional bogs and boggy pools. 



* The details of these collections are being published separately. 



