CRUSTACEAN PLANKTON Ob' THE ENGLISH LAKE DISTRICT. 411 
The Crustacean Plankton of the Englisli Lake District. 
By Robert Gurney, M.A., F.L.S. 
(Platk 23 and 3 Text-figures.) 
[Read 3rd May, 1923.] 
The published information with regard to the Crustncea o£ the Lake District 
is surprisingly scanty. Mr. Seourfield has included all available records in 
his Synopsis of Britisli Entomostraca (1903-4), but naturally dealt only with 
the district as a whole, without comparison of the fauna of the different 
lakes. Miss Pratt's paper on the Entomostraca of Lake Bassenthwaite is 
the only attempt that has been made to give a comprehensive account of the 
Crustacea of any single lake. The phytoplankton, on the other hand, is 
fairly well-known as a result of the work of Messrs. West and of Dr. Pearsall. 
The following account of the Crustacea of the district lays no claim to 
being exhaustive or even to deal with many of the points of special interest, 
but at least it may serve as a groundwork for comparison with other lake 
areas and to draw attention to questions on which further work is required. 
The material at my disposal consists chiefly of a series of plankton samples 
taken by Dr. W. H. Pearsall during 1921 and 1922 for the purpose of a 
study of the phytoplankton, and I wish to express my thanks to him for the 
loan of these collections and for the valuable information which he has 
readily given to me during the course of the work. I have .also myself' 
visited the district and have made collections in a few of the lakes. During 
the autumn of 1922 I spent a week in the western part of the district 
specially investigating the Crustacea of Ennerdale, Wastwater, and Coniston. 
While it is probable that the collections at my disposal give a fairly com- 
plete picture of the composition of the crustacean plankton of the various 
lakes, it is unfortunately true that the methods which are suitable for the 
collection and preservation of phytoplankton are by no means so for the 
Crustacea ; and for this reason, though Dr. Pearsall's collections extend over 
a large part of two years, it is not possible to deduce from them any reliable 
conclusions as to the seasonal distribution and variation of the Entomostraca. 
Undoubtedly much further work remains to be done with regard to these 
two questions, and also in connection with the vertical distribution of the 
species. It seems also to be probable that the distribution of the Crustacea 
may not be uniform in some of the larger lakes, and that such lakes should 
not, therefore, be dealt with as homogeneous units. For instance, the com- 
position of the plankton in the deep part of Ennerdale is not the same as 
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