THE FRESHWATER PLANKTON OF THE SCOTTISH LOCHS. 505 
Var. apicibus semicellularum levissime convexis et glabris, cum serie verrucarum 
emarginatarum circ. 6 intra marginem, angulis in processus verrucosos longos productis ; 
a vertice vise triangulares, lateribus subrectis et glabris, cum serie verrucarum 
emarginatarum circ. 6 intra marginem unumquemque, angulis in processus longos 
verrucosos productis. 
Long. 83; lat. cum proc. 108-115 4; lat. isthm. 20 x. 
Hab.—Loch Fadaghoda, Lewis, Outer Hebrides. 
34. St. forficulatum, Lund. 
Long. 55-57 » ; lat. 54-69 u; lat. isthm. 9°6-13°5 m (PI. 7, fig. 17). 
Hab.—Loch Fadaghoda, Lewis, Outer Hebrides. 
The specimens observed of this rare Desmid were exactly typical, but all were 
tetragonal in vertical view. The species has been recorded from Perthshire, but as no 
British specimen has ever been figured we give a figure of one (PI. 7, fig. 17). 
Genus Sphxrozosma, Corda, 1835. 
ao) 5. Aubertianum, West, in Journ. Bot., xxvii., 1889, p. 206, t. 291, f. 17; in 
mourn. Linn. Soc., bot., xxix., 1892, p. 115, t. 19, f. 1. 
The specimens showed considerable variation, more particularly with regard to the 
relative width of the cells and the form of the semicells. The semicells were mostly 
narrowly oblong or oblong-elliptical in form, and each lateral margin clearly showed 
two granules. In some specimens granules were observed across the front of the 
semicell, the forms thus passing into the var. Archerw (Gutw.), W. & G. S. West. 
Long. 17°5-19 ; lat. 25-27-54; lat. isthm. 5°5-6m; crass. 11°5 u (PI. 6, fig. 7). 
Genus Hyalotheca, Khrenb., 1841. 
36. H. Indica, Turn., in Kongl. Sv. Vet.-Akad. Handl., xxv., 1893, No. 5, p. 152, 
Ee22, fig. 17 (not t. 19, fig. 18). 
Forma, long. 13-15°5 w; lat. 11-12» (PI. 6, fig. 6). 
Hab.—Loch Fadaghoda, Lewis, Outer Hebrides. 
Genus Desmidium, Ag., 1824. 
37. D. coarctatum, Nordst., in Botaniska Notiser, 1887, p. 155; in Kongl. Sv. 
mer-Akad. Handl., xxii., 1887, No. 8, p. 25, t. 2, f. 3. 
Var. cambricum, West, in Journ. Roy. Micr. Soc., 1890, p. 283, t. 5, f. 2. 
Long. 35-40 ; lat. 40-42°5 u; lat. apic. 17°5-20 4; crass. 32-34 u (PI. 6, fig. 5). 
Hab.—Loch Fadaghoda, Lewis, Outer Hebrides. 
The cells were considerably longer than in the specimens observed from Wales, 
and the plant has much of the habit of Desmidiwm graciliceps. 
38. D. occidentale, sp. n. (Pl. 6, figs. 3, 4). 
D. mediocre, filis tortis, sine vagina mucosa ; cellule 14-plo latiores quam longe, 
