424 Proceedings of Royal Society of Edinburgh. [sess. 
also pointed out the very “remarkable scarcity of many of the 
free-swimming Protococcoideae.” Still, it must he remembered 
that these organisms, judging from Chodat’s investigations, could 
by no means he expected, all these plants, except Sphoerocystis and 
a few others, being extremely rare in lakes : the numerous species 
recorded by Lemmermann, Bruno Schroder, and others, all inhabit 
the shallower and warmer lakes (see West, p. 554). 
On the other hand, the explorations of Messrs West have proved 
that the Desmidiacese play a most prominent and remarkable part 
in the Pelagic region of a considerable number of the larger lakes. 
The authors state that the Scottish phytoplankton “ is unique in 
the abundance of its Desmids. No known plankton can compare 
with it in the richness and diversity of the Desmid flora.” In the 
present state of our knowledge, I consider the presence of these 
numerous Desmids to he one of the most peculiar traits in the 
composition of the plankton of the Scottish lakes. As far as I 
know, very few of them have hitherto been recorded in the Pelagic 
region of any of the greater European lakes, and their common 
occurrence is quite the reverse of what might have been expected 
from Chodat’s and my own observations. In the other European 
lakes only two species, viz., Staurastram graciie and S. paradoxum, 
are common. The manner in which, I think, we may endeavour 
to account for their frequent occurrence will he referred to after 
the plankton groups have been treated of. 
As the Flagellata, Heliozoa, and Infusoria have not hitherto 
been specially studied, and I myself have had no opportunity of 
visiting the lakes in the season during which many of the Elagellata 
and Infusoria are generally most abundant, I do not venture to 
deal with these groups in detail, hut restrict myself to the follow- 
ing remarks. I have found Dinobryum in all the lakes explored, 
and in a few instances also species of the genera Mallomonas and 
Gymnodinium. Ceratium hirundinellci seems to he common, and 
the frequent occurrence of Clathrulina is very remarkable — usually 
empty shells, for only once, I think, did I see a living animal. 
As far as one may judge from the investigations of Mr James 
Murray, it seems that the plankton Kotifers are quite similar to 
those in other countries, but the absence of Mcistigocerca capucina 
is remarkable. 
