THE FRESH- WATER LOCHS OF SCOTLAND. 209 



is small, the larger Entomostraca especially being deficient. With this 

 is correlated an unusual clearness of the water (a white disc was visible 

 in June at a depth of 42 feet). The plankton hardly varies throughout 

 the year, except that Leptodora, Bythotrephes, Holopedium, and a few 

 other genera appear in the summer months only. The quantity was 

 slightly greater in March than at other seasons. At no season has 

 Daphnia been observed in the loch, and its absence has also been noted 

 by Dr. Thomas Scott (as long ago as 1892) and by Mr. D. J. Scourfield. 

 This is the more remarkable as Daphnia abounds in Loch an Nostarie, 

 about a mile distant, and discharging into Loch Morar by a con- 

 siderable stream. The only Diaptomus was the common D. gracilis ; 

 while many of the other large lochs in about the same latitude have also 

 one or other of that group of closely related species represented in 

 Loch Ness by D. laticeps. The Bosmina was the typical B. longispina y 

 and not B. obtusirostris, which is the common species in the majority 

 of the Scottish lochs. In contradistinction to the scarcity of larger 

 organisms, many very small species were abundant. Desmids especially, 

 of a few species, were unusually numerous in the plankton at all seasons. 

 A remarkable variety of Xanthidium subhastiferum has been described 

 by Messrs. West from material collected by the Lake Survey. In this 

 the two spines of each side of the semi-cell, instead of lying in the same 

 plane as the semi-cell, are placed side by side on the external angles of 

 the wedge-shaped semi-cell. 



The aquatic plants, growing in the shallow water among the islands, 

 yielded an abundant fauna of microscopic animals, especially of Rotifera 

 and Tardigrada. From among these there have been described two 

 new species of Bdelloid Rotifers. A new water-bear of the genus 

 Echiniscus has also been described. It is distinguished chiefly by having 

 the dorsal plates covered by a large hexagonal reticulation in addition 

 to the usual dots. This species was very numerous in October, and has 

 not yet been met with elsewhere. 



