THE FRESHWATER PLANKTON OF THE SCOTTISH LOCHS. A497 
Zoogonidia were not observed. 
The only other British species is Phexococcus paludosus, W. & G. 8. West, a 
species with ellipsoidal cells which occurs in moorland ditches and pools. ¢ 
Family Dinospryace. 
Genus Dinobryon, Ehrenb., 1833. 
2. D. elongatum, Imbhof., var. wndulatum, Lemm., in Berichte Deutsch. botan. Ges., 
1900, p. 28; p. 516, t. 18, f, 21-22. 
Hab.—Loch an Sgath, Lewis; Lochs Diracleet and Laxadale, Harris, Outer 
Hebrides. 
3. D. cylindricum, Imhof., var. pediforme, Lemm., l.c., p. 517, t. 19, f. 12-14. 
Hab.—This variety occurred in great abundance in the plankton of most of the 
lochs examined. 
Class CHLOROPHYCEA. 
Order GiDOGONIALES. 
Family CipoGontacE&. 
Genus Gidogonium, Link., 1820. 
Numerous sterile species of this genus occur abundantly in the plankton of almost 
all the Scottish lochs, most of them being relatively small species of the genus. The 
filaments are mostly short, and they most probably accumulate in the plankton by 
breaking away from the margins of the loch. 
Order MICROSPORALES. 
Family Microsporacea. 
Genus Microspora, Thur., 1850; em. Lagerh., 1888. 
4. Microspora amena (Kiitz.), Lagerh. Quantities of this alga occurred in the 
plankton of most of the Scottish lochs. The filaments were mostly in a fragmentary 
condition, and the cell-walls were greatly thickened, some of the plants being very near 
M. crassior (Hansg.), Hazen. 
Order CONJUGATA. 
Family ZyYGNeEMACEZ. 
Genus Mougeotia, Ag., 1824. 
Species of this genus are very abundant in the Scottish plankton, especially in the 
lakes at high altitudes. They are mostly species with long and exceedingly narrow cells, 
and they very rarely produce spores. Some of the thicker species exhibit a remarkable 
contortion and coiling of the filaments which we have never observed except in the 
