1907.] 



Fresh-water Algal Flora of Ceylon. 



245 



efficacy of the dark rock-surface as a light-absorber and the consequent 

 shaded character of the water in these deeper pools. The third case is from 

 a pool at Kekirawa shaded by the neighbouring jungle. Of equal importance 

 to Spirogyra are species of Zygnema which generally take its place ; from 

 no other waters in the island have I seen as much Zygnema as in the rock- 

 pools. Mougeotia is completely absent, but in one case a considerable amount 

 of Gonatonema occurred. In other cases filamentous Desmids (fig. 4, F and 

 M) play a great part (species of Besmidium, e.g., B. Aptogonium, Bre'b., 



Fig. 4. — Illustration of the Types of Desmids characteristic of the Ceylon Rock-pools. 

 The figures are intended to show the prevalent type, and in no way aim at giving an 

 exhaustive representation of the great diversity of form presented by the Desmids of 

 these pieces of water. A, Micrasterias apiculata (Ehrenb.), Menegh. var. ( x 250). 

 B, Cosmarium decoratum, West and West ( x 250). C, Micrasterias zeylanica, n. sp. 

 (X250). D, Staurastrum bifidum (Ehrenb.), Breb., side view ( x 330 about). E, Ditto, 

 end-view ( x 330 about). F, Desmidium quadrature, Nordst. ( X 330 about). G, Euastrum 

 zeylanicum, n. sp. ( x 560 about). H, Cosmarium (cf. punctulatum, Breb.) ( x 330 

 about). J, Staurastrum aristiferum, Ealfs ? ( x 330 about). K, Cosmarium pseudo- 

 pachydermum, Nordst. (x250). L, Cosmarium Lundellii, Delp. forma (x250). 

 M, JSphwrozosma secedens, De Bary ( x 560 about). 



B. quadratum, Nordst., B. didymum, Corda, and Sphcewzosma, e.g., S. secedens, 

 De Bary). Besmidium is particularly characteristic of these pieces of water, 

 while other filamentous Desmids (e.g., Hyalotfieca and Gymnozyga) which are 

 common enough in the ordinary lowland pools, are almost or completely 



