60 DR. а, S. WEST ON THE ALGÆ OF 
xxiv. (1901) р. 87. The same form has been observed by Lütkemüiler from 
Central China. 
20. COSMARIUM MONILIFORME, (Turp.) Ralfs, Brit. Desm. 1848, p. 107, 
t. 17. fig. 6. 
Var. LIMNETICUM, И’, & G. 5. West, Monogr. Brit. Desm. iii. (1908) p. 23, 
$. 67. figs. 6, T. 
Long. 49-52 ш; lat. 20-29 y ; lat. isthm. 18 м. (Pl. 5. fig. 15.) 
Hab. Yan Yean Reservoir, in the plankton and at the weedy margins. 
This variety was most abundant in the plankton in March 1907, but it 
reached its greatest profusion among the weeds in July. Chains of four 
individuals were not uncommon. The broad isthmus and the thickened poles 
easily differentiate it from other forms of the species. 
21. COSMARIUM AFFINE, Racib. in Rospraw. Wydz. matem.-pr:yr. Akad. 
тие}. Krakow. ser. 2, xxii, (1892) p. 363, t. 6. fig. 25. 
Var. EXCAVATUM, var. п. (PI. 5. fig. 7.) 
Var. semicellulis ad medium apieis minute excavatis ; membrana glabra. 
Long. 16:4 д; lat. 11-8 №; lat. isthm. 8:5 ш; crass. 9-3 D. 
Hab. Yan Yean Reservoir, at the weedy margins (Mar. 1905). 
22. COSMARIUM TORTUM, Lagerh. 5 Nordst. in Wittr., No 
rdst., et Lagerh. 
Alg. Evsie. no. 1486 (1903), fasc. 35, рр. 16, 17 (cum fig.). 
Forma TRIGONA, f. п. (PI. 5. figs. 3-4.) 
Forma cellulis a vertice visis rotundo-trigonis, angulis levissime producto- 
submamillatis ; membrana delicatissime punctulata. 
Long. 21-24 u ; lat. 15-16 p : lat. isthm. 10 y. 
Hab. Yan Yean Reservoir, in the plankton (Feb.-Apr. 1905, very abun- 
dant ; Jan. and Feb. 1906). 
4 
This small species, which might equally well be placed as Staurastrum 
tortum, is a connecting-link between the genera Cosmarium and Staurastrum. 
The twisting of the cells at the isthmus is a much commoner and more 
marked feature of Staurastrum than of Cosmarium, and the discovery of this 
trigonal form adds weight to the suggestion that the species would perhaps 
be better transferred to the former genus. 
23. CosMARIUM TJIBENONGENSE, G'utw. in Bull. Acad. Sci. Cracovie, Nov. 
1902, p. 591, t. 38. fig. 34. 
Forma minor, semicellulis plus regulariter elliptico-hexagonis ; chromato- 
phoris centralibus eum pyrenoide singulo et lobis compressis radiatis. 
Long. 33 ш; lat. 22-23, ; lat. isthm. 5 м. (РІ. 4. fig. 3. 
