78 Froceedings of the Royal Irish Acadeinn. 



That is to say, it is, above all things, characteristically European. It is 

 usually found in lakes of the plains. Altogether, therefore, it does not lend 

 any particular character to Lough Neagh. 



The Cladocera, however, are very' different. In the first place, we find 

 two species of Bosmina, which rarely occur together, both abundant at the 

 same time. Bosmina longirostris and B. ohtusirostris have been recorded 

 before as occurring together, but this is by no means common, and, as will be 

 seen below, taken together with discoveries in the distribution of the 

 phytoplankton, it is extremely interesting. 



Bosmina ohtiisirostris is an arctic species, and was found in the Scottish 

 lake survey in all but the lowland lakes of the south-east. In these lakes 

 Bosmina longirostris was common. In the Baltic and north European lakes 

 Bosmina ohtusirostris is characteristically absent. As a matter of fact, 

 Wesenberg Lund has divided Europe into three regions on the distribution of 

 the Bosmina species : — 



1. A Northern partly arctic region. — Charactei'ized by presence 



of Bosmina ohtusirostris. Scandinavia, north Eussia, arctic 

 lands. 



2. Central European region. — Characterized by the absence of 



B, ohtitsirostris, whilst B. longirostris is rare, and B. Coregoni 

 is most common. 



3. A southern region. — Where the longispina group attains the 



highest development. 



Thus the Bosmina amongst the zooplankton indicates the same admixture 

 of arctic and central European forms as did the phytoplankton. 



Those Eotifera which we have considered in our counts are remarkable 

 for their cosmopolitan character. Thus, 



Anuraea cochlearis, 



A. aculeata, 



Notholca longispina, 



Triarthra longiseia, 



Polyarthra platptera, 

 are recorded for Greenland, Lapland, and the arctic regions generally, from 

 the central European lakes, and from the alpine lakes. James Murray 

 records most of these forms as general and common in the Scottish lochs ; but 

 Triarthra has not been found in the great lakes, and Anuraea aculeata is very 

 rare, and also absent from the great lakes. Triarthra longisefa is common 

 with us, but Anuraea aculeata is rare — so much for features of distribution 

 from the point of view of latitude. 



