278 THE FRESH- WATER LOCHS OF SCOTLAND 
Ammjpa cochlearis ^ Gosse. General. 
Notholca longispina^ Kell. General. - 
Gastropus stylifer, Imhof. ? Local. 
Ploesovia Jmdsoni, Imhof. Local. 
P. truncatiim^ Levander. Local. 
Protozoa. — Nehela hicomis^ West. Very local. 
Raphidiophrys conglohata (GreefF). ? Local. 
R. pallida, F. E. Schulze. ? Local. 
Clathrulina elegans, Cienk. Local. 
In addition to the 30 species above enumerated, there may be 
some doubt as to whether some of the commonest casual species 
might not be included in the plankton. Sida crystaUina is very 
commonly captured in the open water, though the possession of the 
remarkable sucker would lead one to suppose that it would always 
frequent the weedy margin. Alonopsis elongata is still more 
frequently got in the open water, even of the largest lakes, though 
never in great abundance. Fiircularia reinhardti is quite common in 
the plankton ; but it is such a ubiquitous species, living in streams, 
ponds, and even in the sea. that it cannot be considered proper to 
any situation. Synclioeta : the various species of this genus are often 
reckoned in the pelagic fauna, but they so rarely occur in the larger 
lochs, except near shore, that I regard them as pond species. S. 
tremula is perhaps most frequent in the larger lochs, S. pectmata 
is common in small lochs and ponds, and S. grandis has only once 
been noted. 
Arcella, CypJioderia, and a few other Rhizopods are pretty fre- 
quent in the plankton, but still, I think, casual. 
Of the 30 species in the list it may be said of several of them 
that they are too rare, or too little is known of them, to decide 
whether they are true plankton species in the Scottish lochs. 
Bosmina coirgoni, only known in two of the lochs, is included because 
Dr Wesenberg-Lund gives it as usual in the lake plankton of the 
great Central European plain. Nehela bicornis is included because its 
hyaline character seems to indicate fitness for a pelagic life, and its 
discoverer only found it in the plankton (of Loch Shiel). A single 
example was got in Loch Ness. Two species of Raphidiophrys are 
known to be in Loch Ness from Dr Penard's researches, and one 
species in Loch Rannoch. They may be common. 
The case of Clathrulina elegans is peculiar. It is frequent, 
especially in the great lakes, but is by no means general in its dis- 
tribution. It is usually only the skeletons that are found, rarely 
encysted animals, and only once (in Loch Lochy) were they found 
with the pseudopodia extended. 
