121 MR. G. S. WEST ON THE FRESHWATER ALGJE 
Genus XANTHIDIUM, Ehrenb. 
108. Xanruipium CRISTATUM, Bréb. in Ralfs, Brit. Desm. (1848) p. 115, 
t. 19. fig. 3. 
Forma semicellulis subsemicireulari-trapeziformibus, sinu aperto, spinis 
basalibus paullo reductis (interdum duplicatis ut in X. faseieulato). 
Long. sine spin. 60 и, cum spin. 74 u : lat. sine spin. 46 p, cum spin. 58 u; 
lat. isthm. 15 y. 
Nyasa.—In swamp, Kota Kota (20 June, 1904 ; no. 18). 
Genus ARTHRODESMUS, Ehrenb. 
109. AnrHRoDEsMUs Ixcus, (Breb.) Hass. Brit. Freshw. Alge, p. 357 
(1845); Ralfs, Brit. Desm. (1848) p. 118, t. 20. fig. 4 a-d. 
Var. Катехп, W. & G. 8. West, Alga-l. Yorks. (1901) p. 109.—4. Ralfsii, 
West, in Journ. Linn. Soc., Bot. xxix. (1 892) p. 168. А. Ineus, Ralfs, l. c. 
t. 20. fig. 4 e-A. 
а. Forma semicellulis triangularibus, apice recto, spinis validis variabiliter 
curvatis subhorizontaliter dispositis. 
Long. 20 ш ; lat. sine spin. 16 и, cum spin. 52 y. (РІ. 6. fig. 13.) 
Victoria Nyanza.—In plankton, Bukoba (21 Apr. 1905 ; no. 252). 
b. Forma spinis multe brevioribus. 
Long 1455, ; lat. sine spin. 13 ш ; long. spin. 3:5 и. 
Victoria Nyanza.—Swampy pool near Bukoba (20 Apr. 1905; no. 618). 
This form is almost identical with one observed in the Scottish plankton 
(vide W. & G. S. West, in Trans. Roy. Soc. Edinb. xli. pt. iii. (1905) p. 501 
t. 7. fig. 10). 
Genus STAURASTRU M, Meyen. 
110. Sraurasrrum DICKIEI, Ralfs, Brit. Desm. (1848) p. 123, t. 14. fig. 23. 
Victoria Nyanza.—Among Utricularia, near Entebbe (1 May, 1905; 
no. 620). 
111. STAURASTRUM CUSPIDATUM, Bréb. in Menegh. Synops. Desm. (1840) 
р. 226; Ralfs, l. c. р. 122, t. 21. fig. 1. 
Victoria Nyanza.—In plankton, Bukoba (21 Apr. 1905 ; no. 252). 
112. STAURASTRUM BREVISPINUM, Би. т Ralfs, Brit. Desm. (1848) p. 124, 
t. 34. fig. T. 
Var. INERME, Wille, in Ofvers. К. Vet.-Akad. Еот. 1879, no. 5, p. 52, 
t. 13. fig. 62. 
Forma tetragona : long. 40-43 ш ; lat. 32-38 ш: lat. isthm. 14-17 ТА 
Victoria Nyanza.—In plankton with preceding species (no. 252). 
