182 MR. G. S, WEST ON THE FRESHWATER ALGÆ 
Calothrix cartilaginea should be compared with C. balearica, Born. & Flah., 
and C. juliana, Born. & Flah. From the former it is distinguished by the 
swollen bases o£ its trichomes, which are never decumbent, and by the much 
thinner sheath with no trace of lamellation. The cells are also considerably 
longer. From C. juliana it differs in its thinner stratum of darker colour, its 
narrower, much shorter, and more flexuose trichomes, and its longer cells. 
Genus RIVULARIA, (Roth) Ag. ; em. Thur. 
340. RIVULARIA pura, Roth, Neu. Beitr. р. 273 (1802); Born. & Flah. 
in Ann. Sci. Nat. T sér., Bot. iv. (1886) p. 347. 
Forma: crass. trich. 5:5-7 № 5 crass. heterocyst. 5:5-6 д. 
Tanganyika.—Attached to floating decayed stems, Lofu River (5 Oct. 
1904 ; no. 124). 
341. RIVULARIA GLOBICEPs, sp. п. (Pl. 10. fig. 6.) 
R. thallo parvo, submolle, 1:5-3 mm. lato, calce non indurato, hemi- 
spherieo-globoso, caulibus vetustis affixo; filis confertis pressione facile 
secedentibus ; vaginis hyalinis et amplis, vix conspicuis ; trichomatibus inter 
cellulas constrictis, apice in pilum sublongum attenuatis ; cellulis cylindricis 
inferioribus diametro 11—4-plo longioribus, superioribus similibus vel duplo 
brevioribus, cum granulis paucis magnis; heterocystis magnis globosis, 
singulis vel rare binis, cum nodulo incrassato conspicuo juxta cellulam 
basalem. 
Crass. trich. ad bas. 4:8-6 p crass. heterocyst. 10-12 д. 
Tanganyika.—Attached to old stems and leaves, floating in Kituta Bay 
(24 Aug. 1904 ; no. 74). 
The large size of the heterocysts, which are globular and twice the diameter 
of the trichomes, is one of the most characteristic features of this species. 
The cells are cylindrical and in the basal parts of the trichomes are very long. 
They contain scattered conspicuous granules, which are chiefly located near 
the exterior, sometimes even projecting from the wall of the cell. 
In the size of its trichomes R. globiceps most nearly approaches R. hema- 
tites, Ag., but it is at once distinguished by its smaller and much softer 
colonies, which are not incrusted with lime, by the large size of the hetero- 
cysts, and by the somewhat longer basal cells. 
Genus GL(EOTRICHIA, J. Ag. 
342. GLXOTRICHIA NATANS, (Hedwig) Rabenh. Deutschl. Kryptogamenfi. 
p. 90 (1847); Born. § Flah. l. c. (1886) p. 369. 
Forma thallo bulloso usque ad 15 mm. lato ; vaginis plerumque diffluent- 
