348 XI. DESMiDiACEiE (West). [Micrasterias 



in the middle, though often flattened ; it is also a very much rarer 

 species. 



Huii.LA. — In uliginosis editioribus prope Humpata, Empalanca et 

 Lopollo ; May 1860. No. 15. Etiam inter GonaUmcnia tropinun et 

 Temnogametuni hfifcroKpornni, Morro de Lopollo ; Feb. 1860. No. 172. 



11. XANTHIDIUM Ehrenb. (1834). 



1. X. fasciculatum Ehrenb. Infus. 147-8, t. x. f. 24b (1838) ; 

 Ralfs, Brit. Desra. 114-5 ; W. et G. S. West in Journ. Bot. 1897, 

 p. 88, t. 368, f. 16. 



HuiLLA. — In paludibus exsiccandis ; April 1860. No. 176. 



2. X. cristatum Breb. in Ealfs, 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. 



HuiLLA. — In uliginosis editioribus prope Humpata, Empalanca et 

 Lopollo ; May 1860. No. 15. 



In this variety there are two more spines on each semi-cell than in 

 tyf/ical specimens of X. cnstufnm, 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. trilohiml^iordet. [in Vidensk. Medd. Naturh. Foren. 

 1869, no. 14H5, 230-1, t. iii. f. .35 (1870)], in being more distinctly 

 trilobed with a rectangidar 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-aculeaturn (HnlocantJmm 

 calcarato-aculedtum Hieronymus in Engler, Pflanzenwelt Ost-Afrika, 

 Theil C, 20 (1895)), described from the opposite side of the African 

 continent at about the same latitude. 



12. COSMARIUM Corda (1834). 



1. C. centrotaphridium W. et G. S. West in Journ. Bot. 1897, 

 p. 113, t. 367, f. 3-6. 



HuiLLA.— lu uhginosis editioribus prope Humpata, Empalanca et 

 Lopollo, plagas spongiosas unacum Eriocauloneis, Xyridibus et 

 Utriculariis constituens ; May 18(i0. No. 15. 



The apex is sul^rectangular 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. 'i sublobatum Breb. in Balfs, Brit. Desm. 91, t. xxxii. f. 4 



(1848). 



