422 MR. K, GDRNEY OX THE CRUSTACEAX PLANKTON 
It is clear from the table that the plankton is b)' no means uniform 
throughout the lake either vertically or horizontallj', neither is it the same 
by night and by day. 
The chief component of the plankton is JJiaptovms gracilis, which is 
distributed throughout the lake, but is relatively more abundant in the 
western end than in the deep eastern trough, and has a distinct preference 
for the surface. The figures given for the deep-water samples must be 
discounted to some extent, owing to the fishing of the net going down and 
coming up. It is curious that this species seemed to be present in absolutelv 
smaller numbers on the surface by night than bj'' day. 
Limnocalaniis is also distributed all over the lake, but is found only in 
small numbers in the shallow water. It abounds both on the surface and in 
deep water in the eastern trough, and may greatly exceed J), gracilis in 
nurnbers. Although common at all times on the surface, it is notiienbly 
more abundant during darkness. 
Holopedium gibberum, is only exceptionally found on the surface by day, 
but is common in deep water, and at night forms a large part of the surface 
plankton. 
Bosmina nbtnsirostris, though apparently fairly common at some seasons, 
was almost absent from the hike at the time oF my visit, the few specimens 
taken being in dee[)-water samples. 
A curious feature of the plankton was the appearance of Sida crystallina 
on the surface at night. It was not taken during the day in any collections 
in open water, but occurred in three out of four plankton samples taken at 
night. All these samples were taken at the surface over water 80-120 feet 
deep, the only sample in which Sida was not found having been taken in 
shallow water. The specimens taken were almost all males. 
The Entomosteaca of the Tarns. 
The occurrence of JHaptonms laticeps in Hawes Water and in Goats 
Water (as recorded by Brady) raised the expectation that the fauna of the 
high tarns of the district might prove to include other species representative 
of the arctic-alpine Entomostraca which do not occur in the lakes, and, at 
the end of September 1922, I visited some of these tarns and made 
collections in them and in pools and bogs up to an elevation of about 2000 
feet. The result did not fulfil expectation, since D. laticeps was not found in 
any tarn other than Goats Water. There was also a notable absence of tlie 
northern forms of Harpaticid, with the exception of Canthocamptus cuspi- 
dalus, which seems to be comparatively common in Sj)hagnum in running- 
water where the temperature is low. Nevertheless I think the results are of 
sufficient interest to be given in some detail. The complete list of species is 
shown in tabular form. 
