122 MR. G. $. WEST ON THE FRESHWATER ALGÆ 
in Angola, W. Africa. The Nyanza specimens were relatively a little longer, 
but otherwise precisely similar. 
One of the chief features of this species is the presence between the 
granules of small rounded scrobiculations similar to those of C. margaritatum 
(Lund.), Roy & Biss. ; and I should like once more to emphasize the fact that 
it is the only species of its section in which the hexagons of scrobiculations 
are disposed so that two opposite sides are horizontal. 
Schmidle (in Engl. Bot. Jahrb. xxvi. (1898) p. 27, t. 1. fig. 20) has 
described and figured a Cosmarium from Zanzibar, which he names “С. multi- 
ordinatum, forma," but which is most probably a form of C. decoratum, 
W. & G. S. West. 
102. COSMARIUM QUADRUM, Lund. in Act. R. Sor. Sel. Upsal. ser. 3, viii. 
(1871) p. 25, t. 2. fig. 11. 
Forma granulis paullo minoribus. 
Long. 66 p; lat. 65 ш; lat. isthm. 22 y. 
Nyasa.— Among Algæ on rocks, Nkata Bay (23 June, 1904 ; no. 23). 
This form was very slightly smaller than the original Swedish plants, and 
the granules were rather more numerous and of somewhat smaller size. 
103. COSMARIUM MARGARITATUM, (Lund.) Roy у Biss. in Journ. Bot. xxiv. 
(1886) р. 194.—C. latum, Breb., var. margaritatum, Lund. 
Long. 66 ш; lat. 60 ш; lat. isthm, 19 р. 
Nyasa.—Among Algæ on stones, Domira Day (19 June, 1904 ; no. 17). 
Tanganyika.— п plankton, Lofu River (5 Oct. 1904 : no. 124). 
104, COSMARIUM LACUNATUM, sp. n. 
C. mediocre, circiter tam longum quam latum, profundissime constrictum, 
sinu angusto introrsum  valdissime ampliato (lacunato), isthmo breviter 
cylindrico ; semicellul:e trapeziformes, angulis superioribus et inferioribus 
rotundatis, apice lato recto vel levissime concavo, lateribus leviter convexis et 
sursum divergentibus ; membrana granulata, granulis in seriebus obliquis 
(cire. 14) ordinatis, in ambitu toto semicellularum cum granulis circiter 35, 
punctulis minutis 5-6 circa granulum unumquemque ; a vertice vis anguste 
ellipticæ vel oblongo-ellipticz, polis rotundatis. 
Long. 77 р; lat. bas. semicell. 60-62 №; lat. apic. semicell. 80-86 ш; lat. 
isthm. 22 ш; crass. 37 д. 
Nyasa.—In swamp, Karonga (29 June, 1904 ; no. 32). 
This remarkable Cosmarium is at once distinguished by the form of the 
semicells and the extraordinarily dilated sinus. The granulation is very 
similar to that of С. margaritatum, and, as in that species, small punctulations 
are present between the granules. Excluding the sinus, the outline of the 
semicells very much resembles that of С. biretum, Bréb. 
