192 BATYHMETRICAL SURVEY OF 



found in the district, they were never all found together in one loch, 

 as was commonly the case elsewhere in Sutherland. The Daphnia in 

 most of the lochs was the typical D. lacustris. In one loch this was 

 associated with D. galeata, while in three lochs D, galeata was alone 

 observed. Leptodora was only observed in Loch Skinaskink, and 

 Bythotrephes was not observed at all. 



While the fauna thus offers little that is remarkable, the flora, on 

 the other hand, is notable for the great wealth of Algae, especially of 

 Desmids. Over fifty species of Desmids were observed, and between 

 thirty and forty of these sometimes occurred in one loch. Messrs. 

 West, commentii^g on the Desmid flora of this part of Scotland, state 

 that the plankton is unique in the abundance of its Desmids, and that 

 the most conspicuous of these are of a distinctly western type, being 

 found in Europe only along the extreme north-western coasts, while 

 in North America they are eastern species. The southern and eastern 

 limits of this remarkably rich area in Scotland cannot yet be fixed; 

 in Sutherland it extends right across Scotland. An examination of 

 many hill lochs in Perthshire and in the south of Scotland showed no 

 such rich flora there. When the distribution of the Desmid flora is 

 worked out, it will be of interest to observe whether the area covered 

 by those western species coincides with that occupied by the northern 

 Calanidae, Diaptomus Wierzejskii and D. lacintatus, which are so 

 generally distributed in Sutherland, though they also occur in many 

 spots further south. 



Loch Assynt. The plankton of this loch closely resembles that of 

 the larger lochs in the south, only the typically pelagic Entomostraca 

 and Rotifera being present. It is noticeable that neither Diaptomus 

 Wierzejskii, D. laciniatus, nor Daphnia galeata, species widely dis- 

 tributed in the district and also occurring in many of the large lochs 

 further south, was observed here. The loch further resembles many 

 other large lochs in the presence of numerous skeletons of Clathrulina 

 elegans. The only Rotifer calling for mention is Triarthra longiseta, 

 a species not usual in large lakes. Unlike the other lochs of the 

 district, there were very few Desmids in the plankton. The quantity 

 of plankton was very small. 



Loch Lurgain. The fauna comprised only the usual pelagic species, 

 among which Cyclops strenuus was most abundant. The Daphnia was 

 D. galeata. Diaphanosoma brachyurum was present in some numbers. 

 The flora was remarkable for the number of Desmids, especially of the 

 genus Staurastrum, including the beautiful large species, S. longis- 

 pinum and S. arctiscon. 



Loch Bad a' Ghaill. The somewhat meagre plankton was almost 

 exactly of the type found in deep lochs, differing only in the greater 

 abundance of Rotifera, among which were Plcesoma, Gastropus, and 

 Triarthra. The commonest animal was Cyclops strenuus. About a 



