302 THE FRESH-WATER LOCHS OF SCOTLAND 
detail, except for a few species. Desmids are abundant in the lochs 
of the Highland region, and are of very little importance in the 
Lowland region. As there are few lochs in the Lowland region, 
Desmids are common in the majority of the lochs. In the Highland 
region a few species, usually small and inconspicuous, are generally 
distributed. A much larger number, including the majority of the 
large and beautiful plankton species, are greatly restricted in their 
range. They are in the greatest abundance in the north, in 
Sutherland and Lewis. Messrs West declare the plankton of Loch 
Fadagoa in Lewis to be the richest they ever examined, and Desmids 
are especially abundant in it. Several lochs in Sutherland are but 
little inferior to Loch Fadagoa. These Desmids are fairly repre- 
sented here and there in lochs of the west coast, and some alpine 
lochs of the central counties, Perth and Inverness, have a rich 
Desmid flora. In Ayrshire a few alpine lochs recall the abundance 
of Sutherland. 
Mkrasterias rnurrayi^ West. — Only known as yet in two widely 
separated localities, Sutherland and Ayrshire. The type is in Loch 
an Ruathair, in Sutherland ; a triquetrous variety in Lochs Doon 
and Bogton, Ayrshire, two lochs on the same river. The species 
appears to be very near to, and probably derived from, M. papillifera^ 
Breb. 
M. mahahuleshivarensis^ Hobson, var. ivallichii (Grun.). — The 
distribution of this varietv (the type of the species not being found 
in Britain) is very curious. It is in three lochs of the Tay basin, 
(Lochs Bhac, nan Eun, and Shechernich), three in E. Sutherland 
(Lochs an Ruathair, nan Cuinne, and Leum a' Chlamhain), and two 
in Shetland (Lochs Littlester and Burraland). 
M. radiata^ Hass — M. furcata^ Ralfs. — This species is almost as 
local as M. mahahuleshwarensis. It occurs in a few lochs in Perth and 
Inverness, is generally distributed all over Sutherland, though only in a 
small proportion of the lochs, and extends into Lewis (Loch Fadagoa) 
and Caithness. 
M. conferta^ Lund, var. hamata, Wolle. — Fairly common in the 
north, especially in Sutherland. 
M. apiculata (Ehi\), \?iv. fimhriata (Ralfs). — Common in the north. 
M. hrachyptera^ Lund. — ^Loch Ness ; Sutherland ; and Lewis. 
M. verrucosa^ Bissett. — Though Roy and Bissett have recorded 
this species from many localities in the east, it only once occurred in 
Lake Survey collections, in Loch Ness. 
Xanthidmm subhastiferum, West, var. Murrayi^ West. This 
remarkable Desmid, which should be regarded as a form rather 
than as a variety, is only known from Loch Morar, where it is very 
abundant. Though its form is altogether peculiar, Mr W. West, on 
