140 
THE JOURNAL OF BOTANY 
M. pulyerea (Wood) Migula. Loc. 15 (21 P). Distr. Mostly 
N. Hemisph. 
Yar. incertci (Lemm.) Crow. Loc. 4. Distr. Ear., N. Amer., 
Ceylon. 
Forma elongata Crow. Loc. 4. 
Mertsmopedia Meyen. 
Represented by four species which are common in the North 
Temperate Zone: all occur as occasional colonies scattered in the 
plankton* 
M. elegans A. Br. Loc. 22. Distr. Tropics, N. Hemisph. 
M. glauca (Ehrenb.) Naeg. Loc. 2, 8, 23, 24, 25, 26. Distr. 
General (incl. Ceylon). 
M. tenuissima Lemm. Loc. 14. Distr. Eur., N. Amer., Ant¬ 
arctica. 
M. punctata Meyen. Loc. 27. Distr. Temp. 
C(elospiia:rium Naeg. 
C. dubium Grun. Loc. 14, 17, 21, 28. Distr. Eur., Ceylon. 
C. Kutzingianum Naeg. Loc. 11, 29. Distr. Eur., N. Amer., 
S. Afr., Antarctica. 
C. confebtUxM W. & G. S. West ? Colonies smaller than described 
by W. & G. S. West. 72 p diam. Cells 2 p diam. Loc. 5 (rare). 
Distr. Afr. (Mwangdan River), Ceylon. 
Oscillatoriaceae. 
Well represented in the present collection. A number of species 
well known in the plankton of temperate fresh waters occurs, and 
several which have previously only been recorded as benthonic, but 
which reach such an abundance as detached filaments as to play an 
appreciable part as tycholimnetic plankton. 
The limits of the Oscillatoriacece are agreed upon by most 
authorities. The morphological unit is the tricliome, which in itself 
is unbranched but in the higher members of the group forms multi- 
seriate and even branched filaments by enclosure of several within a 
common sheath. It is, however, the simpler members of the family 
that are the most t} r pical plankton organisms. It is these, too, that 
show active motility; there is thus no reason for assuming that 
the septate condition of the Oscillatorian filament has been developed 
in relation to the benthic habit. The plankton members of the 
group no doubt represent the primitive type, although in many 
instances their actual origin must be looked upon as a retrogression. 
Sptrulina Turpin. 
The two species are found mixed with benthic algae, and thus do 
not belong to the typical phytoplankton. They are not attached, 
as are some of the larger species, and correspond in their morphology 
with the plankton species of Oscillatoria. Arthrospira Stizen- 
berger is not distinct from Spiral ina Turpin, but includes the larger 
species of the latter. The prominent septation in Arthrospira is 
merely due to the larger size of its trichomes; this view is confirmed 
