1908.] 



TJie British Freshwater Phytoplankton. 



175 



Species of Dinobryon are common, especially in the early summer 

 plankton. In the May and June plankton of Crummock Water and 

 Derwent Water Dinobryon cylindricum, var. divergens, completely dominated 

 all other constituents. 



Comparison of precisely similar plankton-samples from the various lakes 

 of the English Lake District shows clearly that the proximity of habitations 

 has a distinct effect on the relative hulk of the plankton. Those lakes which 

 are contaminated, by the presence of numerous dwellings and villages along or 

 near the shores possess a relatively greater bulk of plankton than those free from 

 contamination. The explanation of this fact is most probably the increased 

 amount of nitrates in the water of the contaminated lakes. 



Out of 188 species observed in the phytoplankton, 51 per cent, were 

 Desmidiaceae, 21 per cent, were Bacillarieae, and 9 - 5 per cent. Myxophyceae. 



VIII. Malham Tarx, West Yorkshire. 



This lake is the largest natural sheet of water in Yorkshire and covers an 

 area of 153 acres. It is situated on a limestone plateau at an altitude of 

 1250 feet, and there is an extensive peat-bog at its northern extremity. 



The material was collected by boat on July 23, 1904. 



Out of a total of 20 species observed in the phytoplankton nine were 

 Desmids. Sphcerocystis Schroeteri was very abundant and Volvox aureus 

 rather common. Only one Diatom was observed, and four Blue-green Algae. 

 Ceratium hirundinella was very common. 



The following is a complete list of the species observed : — Mbugeotia sp. 

 (sterile), Gonatozygon monotamium, Cosmarium Botrytis and var. depressum, 

 C. depressum, Staurastrum Avicula, var. subarcuatum, St. brevispinum, St. 

 furcigerum, St. Manfeldtii, St. paradoxum, St. teliferum, Volvox aureus, 

 Bed.iastrum Boryanum, Sphcerocystis Schroeteri, Surirella biseriata, Oscillatoria 

 Agardhii, Microcystis aeruginosa, Merismopedia elegans, Chroococcus limneticus, 

 Ceratium hirundinella, and Beridinium sp. 



IX. The British Biver-planktox. 



The first account of British river-plankton (potamoplanktori) was the 

 comparison of that found in the Upper Biver Bann with that of Lough 

 ISTeagh,* and since then Fritschf bas published an account of the phyto- 

 plankton of the Bivers Thames, Trent, and Cam. We have also examined 



* W. and G. S. West, in 'Rey. Irish Acad. Trans.,' vol. 32, sect. B, part 1, 1902. 

 + Fritsch, in 'Ann. Bot.,' vol. 16, Sept., 1902 ; ibid., vol. 17, Sept., 1903 ; ibid., vol. 19, 

 Jan., 1905. 



