West: Phytoplankton of English Lake District. 119 



that quarter. The June plankton is a Dinobryon-plankton, 

 consisting for the most part of immense quantities of Dino- 

 hryon cylindricufn var. divergens. Peridinium Willei was not 

 vmcommon. Desmids were very scarce, and few species were 

 represented. Rotifers were few. Quantities of the pollen- 

 grains of Pines were present in the plankton. 



5. Bassenthii'aite Water, Cumberland. May 1903. Altit. 

 223 feet. About four miles long by three-quarters of a mile 

 wide. Average depth about 18 feet ; maximum depth about 

 70 feet. This lake is in the extreme north-west of the English 

 lake-area, and lies about two miles west from the summit of 

 Skiddaw (3054 feet). There is doubtless a slight contamination 

 of the water from farms and residences in the vicinity of the 

 lake. Diatoms were the dominant feature of the plankton, 

 the most conspicuous species being Tabellaria flocculosa, T. 

 fenestrata, Synedra pulchella, and Nitzschia palea. Very few 

 Desmids occurred, Spondylosium pulchrum var. planum being 

 the most frequent. Dinohryon cylindricum var. divergens was 

 scarce, as was also Peridinium Willei. There were few Rotifers. 



6. Thirlmere, Cumberland. June 1903. Altit. 553 feet. 

 About three and a quarter miles long by about half a mile 

 broad. In 1894 this lake was first used as the water supply for 

 the City of Manchester, and its level raised 20 feet. It has a 

 maximum depth of about 128 feet, and there is scarcely any 

 possibility of contamination of the water. The June plankton 

 consisted mostly of Crustacea (with an abundance of Nauplii) 

 and Rotifers. Tabellaria flocculosa and T. fenestrata were both 

 common, and were both in the form of chains. The most 

 interesting member of the phytoplankton was Rhizosolenia 

 morsa, some individuals of which had formed resting-spores. 



7. Wast Water, Cumberland. June 1903. Altit. 204 feet. 

 About three miles long by about half a mile broad. It is the 

 deepest of the English lakes, having an average depth of 135 

 feet, and a maximum depth of 258 feet. It contains a very 

 large volume of water, which is practically free from all con- 

 tamination, and rising from its south-eastern shore are the 

 world-famous screes. It receives the drainage from the western 

 side of Scafell (3162 feet) and Scafell Pike (3210 feet), and from 

 the southern slopes of the Steeple, the Pillar, and Kirk Fell. 

 The June plankton contained large numbers of Crustacea and 

 Rotifers. Of the latter, Polyarthra platyptera and Notholca 

 longispina were most conspicuous. The Desmids were few in 



1909 March i. 



