7 oy 
SCOTTISH FRESHWATER PLANKTON. 537 
parietalibus, laxe spiraliter contortis, anfractibus 14-4, pyre- 
noidibus in serie singula numerosis. 
Long. cell. 303-427 pv; lat. cell. 14-16°3 py ; lat. apic. 17-18°5 p. 
Hab. Loch Nan Eun, N. Uist, Outer Hebrides. 
This interesting Desmid occurred in small quantity amongst 
other rare species in the plankton collections from the above- 
mentioned lake. It is distinguished from Genicularia spiro- 
tenia, De Bary, by its narrower and more elongate cells, and by 
the fewer turns (from one and a half to four), and therefore the 
laxer disposition of the two spiral chloroplasts. 
The cell-wall is rough with small sharp granules as in G. spiro- 
tenia and the rough species of the genus Gonatozygon. Each cell 
possesses a prominent nucleus embedded in a small mass of 
protoplasm near its central portion. 
Genus Crosrertum, Nitzsch. 
2. C. Cynru1a, De Not. Desm. Ital. 1867, p. 65, t. 7. f. 11. 
Var. CURVATISSIMUM, var. n. (PI. 14. fig. 3.) 
Var. cellulis plus elongatis et multi incurvatis; pyrenoidibus 
6 in chromatophora unaquaque. 
Lat. 12°5 w; apicibus 88 » inter se distantibus. 
Hab. Loch a Bhursta, Benbecula, Outer Hebrides. 
This variety is much elongated without changing the curvature, 
so that although the apices are only 88» apart, a distance ot 
102, can be measured across the curvature. The curvature 
occupies 210° of are, which is greater than any curvature 
recorded for this genus. 
Genus Evastrum, Ehrenb. 
3. E. verrucosum, Ehrenb.; Ralfs, Brit. Desm. 1848, p. 79, 
t. 11. f. 2. 
Var. PLANCTONICUM, var.n. (PI. 15. fig. 4.) 
Var. sinu late aperto; lobis lateralibus integris, obtuse conicis. 
Long. 90 x3 lat. 91 p; lat. isthm. 19°5 pe. 
Hab. Loch Ruar, Sutherland (J. Murray)! 
This striking variety occurred plentifully in the plankton of 
the above-mentioned lake, and is characterized by the conical 
outstanding lateral lobes with entire margins. With the excep- 
tion of the sinus. which is widely open, the rest of the characters 
are as in the typical form. 
