THE FRESH- WATER LOCHS OF SCOTLAND. 291 



character. Any slight peculiarity in the fauna will be noted under the 

 name of each loch. 



In contradistinction to the absence of western species in the fauna of 

 these lochs, is the occurrence in the flora of several Desmids of the 

 western type. These western Desmids, though less numerous than in 

 districts both to the north and south, are in most of the lochs. 



Loch Gown, North and South. These very shallow basins had an 

 admixture of littoral species in the plankton, and the numerous 

 Desmids included both pelagic and bog species. 



Loch a' Chroisg. The only peculiarities of this loch were the 

 abundance of algae and of the smaller pelagic animals, such as Rotifera 

 and Protozoa. Floscularia pelagica, Rousselet, was abundant. 



Loch Achanalt. Owing to its shallow weedy character, littoral 

 species were more numerous than pelagic ones. A species of Gammarus 

 was of a bright slaty blue colour. Ophridium was abundant on the 

 weeds. 



Loch a' Chuilinn. Among the Rotifera observed were Euchlanis 

 lyra, E. dilatata, and Plcesoma truncatum. The Desmid Staurastrum 

 arctiscon was frequent. 



Loch Fannich. As in most of our largest lakes, there were skeletons 

 of ClathruUna elegans floating in the water. Although this is not a 

 true plankton organism (it lives attached by a stalk to plants), the 

 skeletons have seldom or never been observed during the Lake Survey 

 work except in large lakes, while it has rarely been seen living at the 

 margins of those lakes. The lightness of the skeletons, enabling them 

 to float on fresh water, may serve for the distribution of the species, and 

 small cysts are commonly seen in them. Granting this, their absence 

 from smaller lakes is- still unexplained. The only suggestion I can offer 

 is that the lower specific gravity, resulting from the higher temperature 

 of smaller lakes, may prevent the floating of the skeletons, or that the 

 higher temperature may lead to a more rapid decomposition of the 

 material of which they are composed, and so prevent their accumulation 

 in the water. 



Loch Garve. There was nothing peculiar in the plankton, except 

 the apparent absence of Desmids. 



Loch Luichart. In contrast with the neighbouring Loch Garve, 

 Desmids were here abundant, and other algae were also numerous. 



Loch Achilty. Desmids were numerous, including, among species 

 of the western type, Staurastrum arctiscon and S. jaculiferum. 



Loch Kinellan. Ceratium Jiirundinella was very abundant, of a 

 form with long divergent middle horns. There were also observed 

 Volvox globator, Asterionella with very short rays, a species of Cerio- 

 daphnia, and a few larvae of Corethra. 



Loch Uxsie. Ceratium hirundinella, of the same form as in Loch 

 Kinellan, was the most abundant organism. This was the only loch in 

 the district in which Latona setifera was seen. 



