OF THE ENGLISH LAKE DISTRICT. 415 
Group I. of the lakes of the deep and rocky type agree in the limited number 
of species and the absence of species characteristic of shallow and warm 
waters, and in their predominant zooplankton, while. Ennerdale and Wastwater 
together differ from Buttermere and Crummock in the entire absence of 
JJaphnia. Buttermere and Crummock are characterized by the dominance 
in their plankton of the typical form of DapJinia liycdina. Butj although 
Ennerdale and Wastwater are so alike in physical characters, they differ 
markedly in their plankton, not only in the species found, but in their 
relative abundance. Ennerdale possesses two striking species, Ilolopedium 
(jihherum and Limnocalanus macrurus, which are absent from Wastwater, 
but, on the other hand, lacks both Leptodora kindti and Cyclops abyssorimi, 
both of which are common in Wastwater. Further, Bosmina oUusirostris is 
abundant in Wastwater, while it is an insignificant component of the plankton 
of Ennerdale. It cannot, in fact, be said that the Crustacea indicate any 
greater relationship between these two lakes than between either of them 
and certain lakes in other groups such as Hawes Water, Ullswater, or 
Coniston. In these two lakes Dr. Pearsall's grouping is put sharply to the 
test, for, so far as physical conditions go, two lakes could hardly be more 
alike than these, and their phytoplankton also is very similar. 
The same difficulty is met with in the other groups, though it is true that 
Esthwaite has characters which distinguish it very clearly. It has a very 
varied plankton, which contains the " warm-water " or lowland Crustacea 
iJiaphanosoma bracJii/urum, CeriodapJinia, and Cyclops leiickarti; but its chief 
claim to distinction is the presence (in company with B. ohlusirostris) of 
Bosmina loiiffirostiis, which is a distinctly southern form. Grasmere, except 
for containin-^' Ilolopedium, is very similar to Esthwaite. 
In Group II. it is clear that Hawes Water cannot be classed with Derwent- 
water and Bassenthwaite with regard to their Crustacea. The presence of 
the northern species Diaptomvs laticeps places it in a class apart, its elevation 
of 694 feet giving it almost a position among the mountain tarns. It differs 
also from the other two, possibl}^ for the same reason, in the different race of 
Daphnia inhabiting it, and also in the absence of Sida, Leptodora, and 
Cyclops leuckarti, 
Derwentwater and Bassenthwaite also differ considerably, though forming 
part of one drainage system, for the latter lacks any species of Daphnia or of 
Bosmina, being unique among the lakes in this respect. It is true that both 
have been recorded from it, and that a single specimen of Bosmina obtusi- 
rostris occurred in one sample examined by me; but it is evident that, at the 
present time, neither can properly be included in its fauna. The great 
abundance of Diaphanosoma in the plankton of both lakes is a striking 
feature in common, and the plankton of Bassenthwaite may perhaps be 
regarded as that of Derwentwater, in which certain elements have been 
suppressed. 
