446 MR. R. GURNEY ON THE CRUSTACEAN PLANKTON 
For the reasons given above I have also been unable to study the seasonal 
variation. I have, it is true, made an attempt to d'O so with material fVom 
ConistoD, but the numbers available and sufficiently well preserved are not 
enough to give a satisfactory result. They tend to show that there is a 
variation, but that it is very small. 
The species is found at all times of the year, and, except in Wastvvater 
and the tarns, there seem to be no pronounced sexual periods. Ephippial 
females have been seen in collections from Windermere (Sept and Oct. 1921), 
Crummock (Oct. 1921), Derwentwater (Nov. 1921), and Wastwater (Sept. 
and Oct. 1921 and 1922). In Wastwater alone do ephippial females form 
any considerable proportion of the population. On Sept. 30, 1922, 31 per 
cent, of females were ephippial, but not a single male was seen. In Coniston 
and Ullswater there seems to be no sexual phase. 
BXJSMINA LONGIROSTRIS, 0. F. Muell. 
This species only occurs in Esthwaite and Grasmere, both being lakes of 
the " evolved ■" type ; but, whereas it appears to be the only species of 
Bosmina in Grasmere, in Esthwaite it is found in company with B. obtusi- 
rostris, an unusual association which is also found in Lough Neagh and has 
been commented on by Dakin and Latarche. 
Miss Pratt states that it was common in Bassenthwaite in 1898, but it was 
not found in any of Dr. Pearsall's collections from that lake. Miss Pratt's 
list of Crustacea from Bassenthwaite differs in so many respects from my 
own that one can only conclude that conditions must have changed very 
greatly since 1898. 
The Esthwaite form is quite typical, but in Sept. 1921 the antennse of the 
adults were found to be unusually short, and many were even of the form 
described by Lilljeborg under the name of B. hrerAcornis Hellich. It 
appeared in the collections first in April and increased in numbers till June. 
In July numbers decreased, and in August it was very rare. In September 
it was again , present in abundance, and large numbers of females bore 
ephippia. It was not found in collections made in October and November. 
LiTEEATUEE REFERRED TO. 
Beck, C. — On some new Cladocera of tlie English Lakes. Journ. K. Mic. Soc. (2) iii. 18b3, 
p. 777. 
JiiRGE, E. A.— Plankton Studios un Lake Mendola. XL Trans. Wise. Acad. xi. 1898, 
p. 274. 
Brady, G. S. — Notes on the Crustacean fauna of the English Lakes. Intellectual Observer, 
xii. 1868, p. 416 *. 
Beady, G. S.— British species of Entomostraca belonging to Baphnia and other allied 
genera. Nat. Hist. Trans. Northd. and Durham, xiii, 1898, p. 317. 
I have not been able to consult this paper. 
