540 MR. W. WEST AND PROF. G. S. WEST ON 
t 18. f. 29), from which it differs in its hexagonal semicells, 
closed sinus, and longer spines. 
7. X. TerracentrotumM, Wolle, Desm. U. S. p. 95, t. 22. 
ff. 8,9; West & G. 8S. West, in Trans. Linn. Soc., ser. 2, Bot. v. 
(1896) p. 253, t. xv. f. 24.-Arthrodesmus incrassatus, Lagerh. 
in. Ofvers. af K. Vet.-Akad. Férh. (1885) no. 7, p. 242, t. 1. f. 18. 
A form with a more pronounced central protuberance. (PI.16. 
fig. 7.) 
Long. 58; lat. sine spin. 52, cum spin. 79; long. 
spin. 10°5-15 5p; lat. isthm. 155; crass. 36 p. 
Hab. Loch Laxadale, Harris, Outer Hebrides. 
8. X. SUBHASTIFERUM, West, in Journ. Linn. Soc., Bot. xxix. 
(1892) p. 166, t. 22. f. 4. 
Long. 52-53'5 »; lat. sine spin. 48°5-53°5 yw, cum spin. 81- 
86 »; long. spin. 14-16 w; lat. isthm. 14-16°5 w; crass. 29 pu. 
(Pl. 16. figs. 4, 5.) 
Hab. Loch Ghriar and Loch Nan Cuinne, Sutherland (J. Mur- 
ray)! 
The Scotch specimens of this species were identical in all 
respects with thuse observed from Ireland. A certain amount 
of variability of the spines was noticed, one spine being fre- 
quently reduced or absent (cf. Pl. 16. fig. 5a). The great 
majority of the specimens possessed two equal divergent spines 
placed one above the other. 
Var. Murrayt, var.n. (PI. 16. fig. 6.) 
Var. semicellulis subobsemicircularibus, apicibus truncato- 
convexis, angulis superioribus cum spinis longis geminatis 
subhorizontaliter dispositis. 
Long. 52; lat. sine spin. 50°5-51°5 p, cum spin. 87-894 ; 
long. spin. 18-20 p:; lat. isthm. 17 w; crass. 28 p. 
Hab. Loch Nan Cuinne, Sutherland (J. Murray)! 
Genus Cosmarium, Corda. 
9. C. Lunpetiir, Delp. in Mem. Acead. Sci. Torino, ser. 2, 
xxx. (1878) p. 13, t. 7. ff. 62-64.—C. subcirculare, W. B. Turn. in 
A. Sv. Vet. hat Handl. xxv. (1892) no. 5, p. 52, t. 8. f. 3, and 
t. 9. ff. 27,3 
