298 THE FRESH-WATER LOCHS OF SCOTLAND 
D. wierzejsJcn^ Richard. — The Lake Survey has 30 records of the 
occurrence of this species. It has a much more restricted range than 
D. laciniatiis. and is mainly confined to the extreme northern and 
western fringe of the country. There are 3 records for Sutherland ; 
1 for Caithness ; 2 for Lewis ; 3 for LTist ; 20 for Shetland ; and 1 for 
Ross (strange to say, in the extreme east). The western islands were 
visited when the Diaptomus was in most lochs too young to be iden- 
tified, and Dr Scott's records show that it is much commoner in the 
Outer Hebrides — he notes it in 8 lochs in the small island of Barra 
alone, — and in Shetland he gives many additional localities. Dr Scott 
found it in Mull, which is its southern limit in Scotland ; its eastern 
limit on the mainland is St John's Loch, in Caithness. It is the 
common, and almost the only, species in Shetland, but has not been 
noted in Orkney. It is the only species found in L^ist, except the 
closely related D. laticeps, only distinguishable when fully mature. 
Its general distribution, so far as known, is apparently dis- 
continuous : it occurs in Spain, Germany, and North Russia. In 
altitude it is not known to ascend so high as D. laciniatiis^ the highest 
locality from which I have noted it being Loch Maol a' Choire, in 
Sutherland, 900 feet above sea-level. A great many of the lochs 
where it occurs are very little above sea-level. 
D. laticeps^ Sars. — This is the commonest and most generally 
distributed of the northern species of Diaptomus. Though mainly 
a Highland species, it is recorded from a reservoir near Edinburgh. 
The Lake Survey has 46 records for it — 5 for Perthshire ; 12 for 
Inverness ; 7 for Sutherland ; 2 for Caithness ; 3 for Orkney ; 1 for 
Shetland ; 1 for Ross-shire ; 10 for Lewis ; 3 for Uist ; 1 for Argyll, 
and 1 for Edinburgh. It is found at all elevations, from the slightly 
tidal Loch of Harray, in Orkney, to about 2500 feet in Perthshire. 
Out of Britain I onlv know the species as Scandinavian. 
D. gracUis^ Sars. — The commonest species in Scotland, as in Europe 
generally, its distribution only calls for remark because of the apparent 
total absence from the Shetland Isles and North Uist. In the Orkneys 
it has been noted only in two lochs. 
On the mainland it is almost universal, but is occasionally replaced 
by one of the three northern species {D. lacmiahis, D. laticeps, or D. 
zvierzej skii). Usually it accompanies those species where they occur. 
In only one district, N. W. Sutherland, did it appear to be absent from 
most of the lochs. 
Asellus and Gammarus. — Though both these Crustacea, the largest 
in the lochs, are common, they are seldom found both in the same loch. 
Mysis. — The Mysis in the lochs is apparently a migrant, not a 
relict, and its scattered distribution and rarity are probably deter- 
mined by the scarcity of suitably situated lochs. Only one of the 
