514 MR W. WEST AND MR G. 8. WEST ON 
It is doubtful if the two forms of Asterionella are specifically distinct. A. 
gracillima possesses longer frustules than A. formosa, but it is questionable if there are ; 
any other distinctions between them. They occur as stellate groups, the frustules 
being arranged like the spokes of a wheel. In the centre of. the colony they are joined — 
by minute mucous cushions in a spiral manner, so that there may be up to two and a 
half turns ; that is to say, there is often more than two complete circles of frustules. 
The commonest number of frustules in a circle is eight, but seven and nine occur. 
Some continental authors have observed only three, four, or five in a circle, but the 
Scottish ones contain more than that. Intermediate forms occur. 
Tabellaria fenestrata is very abundant and very variable, especially in the relative 
length and breadth of the frustules as seen in girdle-view. The commonest form is in 
zigzag chains, but the star dispositions (var. asterionelloides) are abundant in some 
lakes. This variety ‘ asterionelloides’ is very variable in itself, as can be seen from the 
photographs on Plates 1 and 2. Sometimes the frustules are short and broad, whereas 
in other cases they are long and narrow; Nos. 1 and 2, Plate 2, are examples of these 
extremes. The frustules are disposed in a spiral after the manner of those of 
Asterionella, and they may complete two circles. The commonest Scottish form is the 
6-rayed one, but the number of frustules completing a circle varies from four to eight. 
Tabellaria flocculosa is also very common in zigzag chains. No stars of this 
species were seen, although they have been recorded by HotmsBor from Norway and by 
Lounp from Denmark. 
There are relatively few Myxophycee in the Scottish plankton. Anabena circinalis 
occurs in most of the lochs, but other species are not frequent. Two sterile species of 
Anabena were observed from Loch Bairness, Inverness. Species of Osczllatoria and 
Lyngbya are quite scarce, and Calospherium and Microcystis are both uncommon. 
The quantity of the plankton in the Scottish lochs is never very great and scarcely 
affects the colour of the water. Asa rule it has no marked periodicity such as occurs 
in many of the shallower lakes of continental Hurope. The slight seasonal variations — 
of the plankton is principally accounted for by the more uniform temperature of the 
surface water than is met with in the continental lakes. There is sometimes a pre- 
ponderance of Diatoms at a time when the Desmids are not so numerous, but this is 
not very conspicuous. The only known plankton elsewhere than in the British Islands 
which approaches the Scottish plankton in the number of its Desmids is the Swedish 
plankton. The Danish plankton is relatively much poorer in Chlorophycee, especially 
Conjugates. This is to be attributed principally to the fact that the geological formations 
of Denmark are mostly of Tertiary Age, and therefore the conditions of environment 
are unsuitable for the existence of a rich Desmid-flora. 
The following is a summary of our knowledge of the phytoplankton of the inland 
waters of the west of Scotland :— 
1. The quantity of plankton is relatwely small at any tume and scarcely affects the 
colour of the water. It exhibits little periodicity, the seasonal variations being 
