BIOLOGY OF THE SCOTTISH LOCHS 
301 
or two occasions they have been abundant in the plankton of the 
smaller lochs. 
Cathy pna Ugona^ Dunlop. — This species appears to be rare or 
extremely local. It is such a peculiar form that it is little likely 
to be overlooked. Where it occurs it is often abundant. 
Colurus tesselatus^ Glascott. — Another species which, though small, 
is unmistakable, and apparently rare. 
Noteus quadricornis, Ehr. — Usually found in very shallow lochs. 
It was, however, pretty abundant in the plankton of Talla Reservoir, 
in the deepest part, within a year of the filling of the reservoir. 
Eretmia cubeutes^ Gosse. — Mr Rousselet, from the side of the 
Rotifera, considers that the Rotifer Eirimia is simply some species 
occupying a Rhizopod shell ; Dr Penard, from the side of the 
Rhizopods, comes to the same conclusion. It would be interesting 
to know what Rotifer does this, and if the combination is habitual. 
From the little I have seen of the dead Rotifers in the shells, I am 
inclined to think that it is some species which normally adopts the 
hermit-crab mode of living. 
Gastropiis stylifer^ Imhof — After the half-dozen species universally 
distributed in the plankton, one of the commonest species is G. 
stylifer. It is very generally distributed ; its brilliant colouring 
causes it readily to catch the eye when present ; it has been noted in 
more than 70 lochs, yet it appears to be to some extent local. 
Phytoplankton 
Phanerogamia. — Stratiotes alokles, L. — The Water-Soldier was 
only observed in the little Loch Fithie, near Forfar, which it almost 
filled in its season, the plants being very large. 
Elodea canadensis^ Miche. — This introduced plant is a pest in 
many lowland lochs. 
Muscinae. — Hypnum scorpioides^ I v. — Though Fon t inalis is the 
commonest littoral moss, H. scorpioides is more frequently submerged 
to a consideral)le depth. In lake-bottoms it is considerably modified 
from the terrestrial form, and is pronounced by Mr H. N. Dixon and 
M. Cardot to be very near to var. mkpielonense^ Ren. and Card. The 
specimens submitted to those specialists were from Loch Ruthven. 
A. similar form from the Peerie Water, in Orkney, is considered by 
Mr Dixon to be an undescribed variety. 
Floridese. — Sacherki { — Lemanea). — This curious plant, which 
usually affects running water, has been twice seen in Scottish lochs — 
abundantly at the overflow of Loch Vennachar, and sparingly in 
Loch Ness, on submerged rocks at Port Clair. 
Desmids. — ^The distribution of the Desmids will not be traced in 
