a 
& 
_& 
Py 
SCOTTISH FRESHWATER PLANKTON. 045 
19. StraAURASTRUM MUCRONATUM, Ralfs, in Jenner, Fl. Tun- 
bridge Wells, 1845, p. 192; in Ann. § Mag. Nat. Hist. xv. (1845) 
p- 152, t. 10. ff. 5, 6 — West § G. 8S. West, in Trans. Roy. Irish 
Acad. xxxii. sect. B, part 1 (1902) p. 44, t. 2. f. 31. 
Var. SUBTRIANGULARE, var. n. (PI. 17. fig. 11.) 
Var. major, sinu apertiore, semicellulis cum dorso subrecto 
vel leviter convexo et ventre subsemicireulari. 
Long. 38°5 py; lat. sine spin. 42-44 un, cum spin. 51-53°5 p 5 
long. spin. 3°8-4°6 w ; lat. isthm. 9°5 p. 
Hab. Loch Doon, Ayrshire. 
20. 8. Dicker, Ralfs, Brit. Desm. 1848, p. 123, t. 21. f. 3. 
Var. RHOMBOIDEUM, var.n. (PI. 16. fig. 9.) 
Var. semicellulis distincte rhomboideis, spinis valde incur- 
vatis. 
Long. 37 w; lat. sine spin. 38°5-46 p ; long. spin. 6-9°5 p; lat. 
isthm. 8°5 p. 
Hab. Loch Nan Eun, N. Uist, Outer Hebrides. 
21. S. cusprparum, Bréb. in Menegh. Synops. Desm. 1840, 
p- 226; Ralfs, Brit. Desm. 1848, p. 122, t. 21. f. 1, t. 33. f 10. 
Var. MAximuM, West, in Naturalist (1891), p. 247. 
Long. sine spin. 32-345 p; lat. sine spin. 24-25°0 py; long. 
spin. 15-17 p; lat. isthm. 3°5-7 p. (Pl. 17. fig. 13.) 
Hab. Loch Shin, Sutherland. Loch Mor Bharabhais, Lewis ; 
and Loch Nan Eun, N. Uist, Outer Hebrides. Loch Katrine 
and Loch Achray, Perthshire. 
This variety was very abundant in some of the plankton 
collections and also very variable. In most of the examples the 
spines were curved outwards, sometimes only a little, but often 
very much. 
The different forms of this variety seem to embrace the 
var. longispinum, Lemm. (Botan. Centralbl. Bd. Ixxvi. 1998, 
p. 4 sep.). 
22. 8. toneispinum Arch. in Pritch. Infus. ed. 4, 1861, 
p. 743.—Didymocladon ? longispinum, Bail. 1851. 
Long. 90-101 »; lat. sine spin. 73-82 p; long. spin. 9°5-32°5 p. 
Hab. Loch Nan Eun, N. Uist, Outer Hebrides. 
The spines of this species vary much in length, and all inter- 
mediate stages are met with between the long-spined typical 
