348 xi. desmidiace^e (West). [Micraaterias 
in the middle, though often flattened ; it is also a very much rarer 
species. 
HtTILLA. — In uliginosis editioribus prope Humpata, Empalanca et 
Lopollo ; May 1800. No. 15. Etiam inter Gonatonema tropicum et 
Temnogametum heterogpanirrt, Morro de Lopollo ; Feb. 1801). No. 172. 
11. XANTHIDIUM Ehrenb. (1834). 
1. X. fasciculatum Ehrenb. Infus. 147-8, t. x. f. 246(1838); 
Raits, Brit. Desm. 114-5 ; W. et G. S. West in Journ. Bot. 1897, 
p. 88, t. 368, f. 16. 
Huilla. — In paludibus exsiccandis ; April 1800. No. 176. 
2. X. cristatum Breb. in Ralfs, Brit. Desm. 115, t. xix. f. 3 
(1848). 
Var. tropicum W. et G. S. West in Journ. Bot. 1897, p. 88, 
t. 368, f. 15. 
Hiili.a. — In uliginosis editioribus prope Humpata, Empalanca et 
Lopollo ; May 1800. No. 15- 
In this variety there are two more spines on each semi-cell than in 
typical specimens of A', cristatum, and the semi-cells are of a somewhat 
different form ; it may perhaps be another species. 
3. X. subtrilobum W. et G. S. West in Journ. Bot. 1897, 
p. 88, t, 368, f. 14. 
Pungo Andongo.— In stagnis prope Anbilla (Condo) ; March 1857. 
No. 177- 
It differs from X. trilobum Nordst. [in Vidensk. Medd. Naturh. Foren. 
1869, no. 14-15, 230-1, t. hi. f. 35 (1870)], in being more distinctly 
trilobed with a rectangular sinus between the terminal and lateral 
lobes, in the lobes being more rectangular, in the presence of a spine 
in the middle of the outer margin of each lateral lobe, in the absence 
of crenulation at the inferior angles of the latter, in the rectangular 
polar lobe having but one spine at each angle (as seen in vertical 
view), and in the narrower vertical view with a more prominent 
central protuberance. 
This species is closely allied to X. calcarato-aculeatum ( Holocanthum 
calcarato-aculeiitvin Hieronymus in Engler, Pflanzenwelt Ost-Afrika, 
Theil C, 20 (189. r >)), described from the opposite side of the African 
continent at about the same latitude. 
12. C0SMARIUM Corda (1834). 
1. C. centrotaphridium W. et G. S. West in Journ. Bot. 1897, 
p. 113, t. 367, f. 3-6. 
Huilla.— -In uliginosis editioribus prope Humpata, Empalanca et 
Lopollo, plagas spongiosas unacum Eriocauloneis, Xyridibus et 
Utriculariis constituens ; May 1860. No. 15. 
The apex is subrectangular with a broad elevation at each angle, 
and another elevation in the centre, the latter not being as high as 
those at the angles. The four pairs of scrobiculations are somewhat 
variable (cf. loc. cit. t. 367, f. 4-6) ; sometimes there are three in 
place of either or both of the two central pairs. 
2. C. sublobatum Arch, in Pritch. Infus. 731 (1861). 
E. % sublobatum Breb. in Ralfs, Brit. Desm. 91, t. xxxii. f. 4 
(1848). 
