THE FRESHWATER PLANKTON OF THE SCOTTISH LOCHS. 503. 
plerumque furcatis (dente unoquoque obtuso) vel interdum integris et obtusis; a 
vertice vise 4-vel 5-radiatee, processibus tam longis quam latitudo corporis; membrana 
glabra ; pyrenoide singulo magno in chromatophora unaquaque ; processibus alterius 
semicellulee cum iis alterius alternantibus. 
Long. sine proc. 31—37 u, cum proc. 40-44; lat. sine proc. circiter 20-22 u, cum 
proc. 53-61 4; lat. isthm. 15—-15°5 mu. 
Hab.—Loch Fadaghoda, Lewis, Outer Hebrides. 
In the nature of its processes this species is precisely similar to certain forms of St. 
brachiatum, Ralfs, but it differs from that species in the shape of its body, its slight 
constriction, and in the radiate character of the vertical view. ‘The processes are 
variable in character, even on the same specimen. They are usually bifurcate at the 
extremity, each lobe being rounded, but sometimes they are obtuse and entire. 
It is unquestionably nearest to St. nudibruchiatum, Borge (Archiv for Botanik 
af K. Sv. Vet.-Akad., 1903, p. 109, t. 4, f. 20), from which it is distinguished by 
the fewer number and different shape of the processes, which possess rounded (not 
acute) apical teeth, and by the smooth cell-wall. The processes of the Scottish species 
are gradually attenuated from the base towards the apex, whereas those of St. 
nudibrachiatum are distinctly constricted at the base and widest in the middle. 
"St. subnudibrachiatum should also be compared with St. Clever (Wittr.), Roy & 
Biss., from which it differs in the processes of each semicell being all in one plane, in 
their rounded apical teeth, in the broader isthmus, and other features. 
Most of the specimens were inclosed in a wide mucous investment. 
25. St. Clever (Wittr.), Roy & Biss., in Ann. Scot. Nat. Hist., 1893, p. 179. 
[ St. lzve, Ralfs, var. Clever, Wittr., in Nova Acta Soc. Upsala, ser. 3, vii. p. 18, t. 1, 
feo. St. Kitchellu, Wolle, 1882, Desm. U.S., 1884, p. 150, t. 40, figs. 35, 36; W. 
&G. 8. West, in Journ. Linn. Soc., bot., xxxiii., 1898, p. 319, t. 18, figs. 10, 11.] 
Long. sine proc. 32”; cum proc. 61; lat. cum proc. 52-57; lat. isthm. 
mY m. 
Hab.—Loch Fadaghoda, Lewis, Outer Hebrides. 
27. St. Tohopekaligense, Wolle, 1885; Hreshw. Alg. U.S., 1887, p. 45, t. 59, figs. 
4,5. [St. nonanum, Turn., in Kongl. Sv. Vet.-Akad. Handl., xxv., 1893, No. 5, p. 
119, t. 15, fig. 14.] 
Var. trifurcatum, W. & G. 8. West, in Trans. Linn. Soc., bot. ser. 2, v., 1895, p. 
Mumeeo, 1. 8; vi., 1902, p. 181, t. 21, f. 27. 
_ Long. sine proc. 38“, cum proc. 61; lat. sine proc. 28, cum proc. 574; lat. 
isthm. 14 « (Pl. 7, fig. 7). 
Hab.—Loch Fadaghoda, Lewis, Outer Hebrides. 
This Desmid has not previously been recorded for the Patch Islands. The Scottish 
specimens exhibited variation in the apices of the processes. Those of the lower whorl 
were invariably trifurcate, but some of those of the upper whorl were often only 
bifureate. 
