246 Dr. F. E. Fritsch. On the Subaerial and [Jan. 2, 



wanting. The unicellular Desmids show similar characteristic features ; thus 

 species of Closterium are either entirely absent or at least rare, and when 

 present they are mostly not those species which are found in the other low- 

 land pools ; Euastrum is also much rarer than in the latter, hut E. dicleltoides, 

 West and West and E. zeylanicum, n. sp.* (fig. 4, G) were rather abundant 

 in one case. On the other hand, species of Micrasterias, which are rare 

 in the ordinary pools, play a great part in these pieces of water (e.g., 

 M. apiculata, Menegh., M. zeylanica, n. sp.,t fig. 4, C, etc.), whilst species of 

 Staurastrum (e.g., S. hifidum,, Breb., S. aristiferum, Ealfs ?) and Gosmarium 

 (G. decor atum, West and West, C. joseudopachyclermum, Nordst., G. Lundellii, 

 Deip., C. punctulatum, Breb. ?) are strikingly abundant in contrast to their 

 scarcity in the clayey pools. Pleurotcenium (P. Trabecula) is sometimes to be 

 found in some quantity. Looking at the Desmid-flora of the rock-pools in its 

 entirety, one is struck by the complexity of form of the diverse species in 

 contrast to the relatively simple forms assumed by the Desmids of the ordinary 

 lowland pools. This feature is illustrated both by the unicellular and 

 filamentous species (cf. figs. 3 and 4), and is certainly very noteworthy 

 (possibly due to aeration of the water ?) As already mentioned, numerous 



* Diagnosis. — Euastrum zeylanicum, n. sp. : — Cells small, about one and a-half times 

 longer than broad, very deeply constricted. Apical incision first slightly widened and 

 then narrowed to more or less of a point. Semi-cells pyramidate, with pointed basal 

 angles ; apex convexo-truncate, the margin on either side of the apical incision being 

 straight or slightly curved. Lateral margins with two incisions, of which the one next 

 the apex is deeper than the other ; upper portion of lateral margins (i.e., part between the 

 apex and the first lateral incision) retuse ; portions of lateral margins between first and 

 second incisions and between second incision and median sinus denticulate. Median sinus 

 very narrow and closed, slightly dilated at its inner end. Cell-wall smooth. Zygospore 

 not seen. 



Length 45 — 50 fx, breadth 30 — 35 fx, breadth of apex 16— 18 fx, breadth of isthmus, 8 p. 



E. zeylanicum has some points of resemblance to species like E. radiatum, Turn., and 

 E. serratum, Josh., but the differences are perfectly obvious. 



+ Diagnosis. — Micrasterias zeylanica, n. sp. : — Cells small, length generally slightly 

 exceeding the breadth, rather deeply constricted ; sinus open, triangular acuminate with 

 a pointed inner termination ; semi-cells three-lobed, lobes separated by incisions, which 

 penetrate as deeply as the sinus, and are inclined towards the latter ; ends of terminal 

 lobe bluntly pointed ; lateral lobes with two blunt processes, separated by a narrow and 

 rather shallow, rounded depression, the process next to the sinus being horizontal, the 

 other bent down towards the sinus ; polar lobe widely spreading, slightly drawn out at 

 each extremity into a horizontal or deflected process ; apex flatly convex. Outline very 

 faintly granular. Cell wall smooth or minutely punctate. Zygospore not seen. 



Length 60 — 65 /*, breadth 55 — 60 /z, breadth of polar lobe 50 — 55 fx, breadth of isthmus, 

 15— 18 /x. 



Micrasterias zeylanica belongs to that group of species which includes M. oscitans, Ealfs, 

 and M. incisa, Ralfs, but is more complex than either of these. In this respect it comes 

 nearer to M. truncata (Cor da), Breb., which is, however, much more abundantly incised. 



