Entomostraca of Lake Bassenthwaite. 469 



Bassenthwaite Lake is particularly well suited for faun is tic 

 investigations, for while being one of the lowest of the English 

 lakes, it lias the largest drainage-area ; it also receives the 

 overflow from Derwentwater and Thirlmere ; therefore in 

 Bassenthwaite we should expect to find a typical lake-fauna, 

 and, in addition, a concentration of the forms living within 

 the drainage-area of the lake. 



Bassenthwaite* is the same size as Derwentwater — a little 

 over 2 square miles in area. It is 3"83 miles in length, its 

 average breadth is "054 mile or 950 yards. The widest part 

 of the lake is exactly f mile. The surface of the lake is 

 223*4 feet above the sea-level ; the average depth is 18 feet ; 

 the greatest depth is 70 feet. Direct drainage-area 91 \ square 

 miles ; total catchment-area 134 square miles. 



The upper end of the lake is shallow, and depths over 

 25 feet are confined to a trough nearly 2 miles long in the 

 middle of the lake. The section across the lake suggests 

 a double-troughed depression separated by a broad central 

 rise. Mill says: — " The steep slopes of the lake above and 

 below water were always composed of smooth rounded stones, 

 much smaller than the great blocks of Derwentwater; the 

 stones were only observed to be covered with mud on the 

 shallow flats at the north-west and southern ends, and except 

 for some rushes and water-lilies in the south-eastern corner, 

 there were remarkably few water-plants, and no signs of a 

 ppaty floor. Well out in the lake the sediment was always 

 tound to be soft mud." The soundings were taken on June 

 24th and 26th, 1893. 



On 4th April, 1897, a few tow-nettings were roughly made 

 in the lake, with the view of ascertaining the nature of the 

 fauna. The following forms were taken: — Copepoda : Dia- 

 ptomns castor, Cyclops strenuus, and G. signatus were fairly 

 common; Cyclops ajjinis was rather rare. Daphnid^e : Bos- 

 •nana loiglrostris and the larva} of Leptodora hyalina were 

 fairly common. 



On 21st and 22nd April, and 15th, 16th, and 17th June, 

 1898, the investigations wire more thorough, and the middle 

 and northern portions of the lake were carefully worked at. 



In April ten tow-nettings were taken, six at the surface 

 and four at a depth of from 5 to 6 feet. The preservatives 

 used were (1) a solution of corrosive sublimate, and (2) a 

 mixture of formol, spirit, and osmic acid ; the latter obtained 

 better results than the former. 



On 21st and 22nd April, 1898, it was noticed that the 



* For a complete description of Lake Bassenthwaite see 'Bathv- 

 nietrical Survey of the English Lakes,' by II. R. Mill, D.Sc. 



