500 MR W. WEST AND MR G. 8. WEST ON 
b. Cells large, slightly angular at the apices; cell-wall smooth. Long. 37-52 u ; 
lat. 19-27 uw; lat. isthm, 12-14°8 » (PI. 7, figs. 4, 5). 
Hab.—Loch Fadaghoda, Lewis, Outer Hebrides. 
15. C. abbreviatum, Racib. in Pamietnik. Wydz. matem.-przy. Akad. Umiej. Kra- 
kow, x, 1895, p. ee; calle ale. 
Var. planctonicum, var. nu. [C. abbreviatum, var. W. & G. 8S. West, in Journ. Linn, 
Soc., bot., xxxv., 1903, p. 7541, t. 15-f. 6], 
Var. major, angulis superioribus rotundatioribus. 
Long. 19-29»; lat. 22-30; lat. isthm. 5°5-8 u; crass. 10°5—-13°5 pm. 
Hab.—Loch Tay, Perthshire ; Loch Morar, Inverness ; Lochs Luichart and Rosque, 
Ross ; Lochs Cuthaig, Fadaghoda, Roinebhall, an Sgath, and Loch near Cearnabhal, 
Lewis, Outer Hebrides. 
This variety appears to retain its characters very constantly, and we have only 
observed it from the plankton. It is fairly common in the Scottish plankton, and we 
have previously recorded it from Loch Shin, Sutherland, and from Loch Mor Bharabhais, 
Lewis. 
16. C. capitulum, Roy & Biss., in Journ. Bot., xxiv., 1886, p. 195, t. 268, f. 9. 
Var. grenlandicum, Bérgesen, Ferskv. alg. Ostgronl., Meddelsen om Grrénl., 18, 
Kjébenhavn, 1894, p. 16, t. 1, f. 5. 
Long. 19-21; lat. 16°4-19°5; lat. isthm. 7°7-8°6m; crass. 113 (PI 
figs, 2, 3). 
Hab.—Loch Morar, Inverness; Lochs Cuthaig and Roinebhall, Lewis, Outer 
Hebrides. 
The specimens observed were all slightly smaller than those which have already been 
recorded as occurring in the plankton of Loch Doon, Ayrshire. 
17. C. Botrytis (Bory.), Menegh. 
Var. depressum, var. n. (Pl. 7, fig. 1). 
Var. cellulis circiter tam longis quam latis, angulis basalibus semicellularum latioribus 
et rotundatioribus, angulis superioribus obtusissimis. 
Long. 68-72 »; lat. 65-68 4; lat. isthm. 16-17 nu. 
Hab.—Loch Ruar, Sutherland (J. Murray)! 
This variety occurred in quantity in the plankton of the above-mentioned loch. Ié 
seems well characterised by its depressed semicells, which easily distinguish it from any 
other variety of C. Botrytis. 
Genus Xanthidiuwm, Ehrenb., 1834. 
18. X. antilopaum (Bréb.), Kiitz. 
Var. Hebridarum, var. n. (PI. 7, fig. 21). 
Var. cum spinis tribus supra marginem superiorem semicellule uniuscujusque utro- 
bique, spina singula ad angulum superiorem et spinis duobus prope angulum lateralem 
