GL 
SCOTTISH FRESHWATER PLANKTON. 503 
Genus Borryococcus, Kitz. 
41. B. supericus, Lemm. in Forschungsberichte Biol. Stat. 
Plon, iv. 1896, p. 111, cum fig. 6 u. 7. 
Var. pLANCTONICUS, Lemm. in litt. 
Cellule globose, 7-9 w crass, in familiis globosis vel oblongis 
consociate. 
Hab. Loch Shin and Loch a Gharbh Bhaid Mhoir, Sutherland. 
The cells are much smaller than in typical B. sudeticus. 
We think it most probable that both this variety and the type 
are merely forms of B. Braunii, Kiitz. 
IV.—ConcuvsIons. 
1. The Scottish phytoplankton differs considerably from that 
of the western parts of continental Europe. 
2. It is unique in the abundance of its Desmids. No known 
plankton can compare with it in the richness and diversity of the 
Desmid-flora. 
3. The most conspicuous of the Desmids are of a distinctly 
western type,—a type confined almost exclusively to the extreme 
western and north-western shore-districts of Europe and to North 
America. This type of Desmid is known from the west of 
Scotland, Ireland, and Wales, also from Scandinavia, and in 
some cases from Lapland ; it is well represented by Staurastrum 
longispinum, S. brasiliense var. Lundellii, S. curvatum, S. jacu- 
liferum, S. anatinum, S. Ophiura, S. verticillatum, S. Aretiscon, 
Micrasterias furcata and M. conferta, and to a less extent by 
Staurastrum sexangulare, S. aversum, S. lunatum var. plancto- 
nicum, and §. megacanthum. 
These Desmids which occur in the plankton are also known to 
us from the bogs and rocky pools of North-west Scotland and the 
Outer Hebrides, and it is of surpassing interest that they should 
have this exclusive European distribution and at the same time 
be frequent in the eastern parts of the United States and in 
Nova Scotia. Certain of these species are also known from the 
Faroe Islands and trom Iceland. 
4. The commonest and most abundant Desmids of the plankton 
are invariably species of the genus Staurastrum ; and the two 
most abundant species are S. paradoxum var. longipes and 
S. jaculiferum. 
5. One of the most suprising features is the abundance of 
