FRESHWATER PLANKTON ALG.E FROM CEYLON 
165 
guish a definite variety. Loc. 2, 3, 4, G, 9, 10, 11, 18, 24, 25, 2G, 
27, 31, 35, 37, 38, 41, 42, 43, 44, 47, 48 (rare), 50, 51, 52, 53, 5G, 
58, 59. JJistr. Cosmopolitan (incl. Ceylon). 
Dictyosphaeriaceae. 
Westell a. 
W. eotryoides (W. West) de Wildeman. Loc. G. Distr. 
Eur., N. Amer., Afr. 
DlCTYOSPIIJmiUM. 
D. Egrenbergianum Naeg. Loc. 2, 4, 5, 10, 23, 49, 54. 
Distr. Eur., N. Amer., Afr. 
Dimorphococcus. 
I). Fritschii Crow, in Ann. Bot. xxxvii. no. clxv. Jan. ’23, 
pp. 141-145. Loc. 1L, 24, 27, 32, 56. 
Oocystaceae. 
Oocystis Naeg. 
O. crassa Wittrock. Some of the specimens from Tank Magas- 
wewa diverged slightly from the type. Variants apparently inter¬ 
mediate between the type and O. Marssonii Leinm. were observed ; 
in these the cells were 12-15 p in length and sometimes nearly as 
wide, thus even in side view approaching a circular outline. This 
latter feature is characteristic of O. Marssonii, but in O. crassa the 
cells are nearly twice as long as wide. There were apparently 3-4 
chromatophores in the cells, which seemed to be well preserved. In 
O. crassa there are normally 4-8 chromatophores; in O. Marssonii 
1-2. Brunnthaler (in Pascher’s SusswasserH.) considers the latter 
closely related to it if not identical with O. crassa , whilst Printz in 
his recent monograph regards it as a variety. The specimens from 
the other localities were few; one measured from Tank Andan- 
kulam had the rather unusual dimensions of 29pxl2p; the rest 
were of the normal type, and fell within the dimensions given by 
Brunnthaler—14-2G p in length, 10-20 p in width. Loc. 4, 9, 29, 
37. Distr. Eur., N. Amer., Ceylon. 
Scenedesmus Meyen. 
The occurrence of this in the plankton may be contrasted with 
that of Oocystis. The numerous species recorded below are quite 
abundant even in the larger pieces of water, in this agreeing with the 
position in other parts of the world, and the plakea type of colony 
seen in Scenedesmus is doubtless in some way related to the free boat¬ 
ing habit of the plant. The species recorded below are mostly 
common as facultative planktonts in other parts of the world. They 
are morphologically the most highly differentiated types, nearly all 
showing marked tendency towards the spindle-shaped cell-form and 
often having spines, teeth, or other ornamentation ; dimorphism of 
the cells is frequently well marked. 
S. obliquus (Turp.) Kuetz. Loc. 44. Distr. General (incl. 
Ceylon). 
