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 Baphnia 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, 
and not B. ohtusirostris, 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 subliastiferum 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 Hotifera 
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. 
p 
