334 Notes on the Blue-green Alga, etc. 
3. Capitate or sub-capitate ; stratum dark-coloured, O. irrigua 
Trichomes 6-11 mic. in dia., straight, 
not torulose; apex not tapering; cells 
4-11 mic. long; * apical cell convex with 
thickened membrane. In stagnant or 
running water, ditches, etc. (G. 218, 6, 
22,123) 
3. Not capitate 
4. Very acute 
4. Sometimes more rounded at apex or conical. 
. Capitate or sub-capitate é a8 
. Not capitate or only very slightly so 
an 
6. Not more than 4 mic. in dia.; cells usually ¢ equal 
to or longer than the diameter 
6. More than 4 mic. in diameter; cells usually 1 much 
shorter than the diameter, occasionally longer 
7. Trichomes 3-5 mic. in diameter ae O. acuminata 
Stratum bright blue-green ; trichomes 
straight, fragile, constricted at joints; 
apex tapering, curved, rarely straight ; 
cells 5-5.8 mic. long, trans. walls with 
granules; apical cell sharply pointed. 
In warm salt water. (G. 247, 7, 12; 
WS Gfsky ai, 28h) 
7. Trichomes 6-8 mic. in diameter oe or O. janthiphora 
Trichomes dark green, straight, fragile, 
not constricted at joints; apex tapering, 
curved or lax spiral; cells 3.4-6-7 mic. 
long, trans. walls slightly granular ; 
apical cell sharply pointed. (G. 233, 7, 
20-21.) 
8. Trichomes 1o or more than Io mic. in diameter, or 
variable 4-11 mic. in diameter : of 
8. Trichomes g or less than 9 mic. in diameter .. 
g. Length of cells nearly equal to or longer than the dia- 
meter, always more than half the diameter 
g. Cells distinctly shorter than their diameter. . 
10. Torulose or constricted. . ae 
10. Not torulose 
11. Trichomes more than 10 mic. in 1 diameter ; length of cells 
not more than a quarter of the diameter. . 
11. Trichomes usually less than 10 mic. in diameter; cells 
longer than a quarter of the diameter, sometimes as 
long as or longer than the diameter 
12. Trichomes never less than tomic. in diameter, 
often much more 
12. Filaments 5+5-II mic. in diameter .. P. subfuscum 
Stratum a thin, dark green or olive green 
mass ; trichomes fragile, straight, not con- 
stricted at joints, agglutinated; apex 
capitate, not curved, slightly tapering ; 
calyptra conical; transverse walls with 
cyanophycin granules; On wood, rocks, 
etc., in fresh water. (G., 182, 5, 17-20; 
W. o5; 35; ens) Varreex ane eWVar: 
joannianum, see G., p. 184. 
IQ: 
20 
*The measurements of length ae breadth of the cells and filaments. 
are given in microns. A micron = ;z%4, of a millimetre, or about g5$pq Of 
an ick 
Naturalist, 
