153 ULOTHRICACEAE 
of U. zonata. When kept in stagnant water the chromatophore 
‘becomes reduced to a small plate, and the filament looks very 
much like that of U. variabilis. From the latter, however, it 
seems always to be distinguishable by its greater diameter. It 
might seem at first sight that this is only a large form of U. vari- 
abilis, but from careful observation of the living plants the points 
of distinction are convincing though not easily described. 
The plant did not make its appearance in the two stations 
where we have observed it earlier than August, and probably not 
until during September. The chromatophores seemed to be some- 
what injured by the first frosts ; whether the plant would have 
been killed before winter could not be determined, because of the 
fact that the water was drained from both basins at the approach 
of cold weather. 
6. ULOTHRIX VARIABILIS. (Kütz.) Kütz. Spec. Alg. 346. 1849; 
Tab. Phyc. 2 : 22 62.7. 3. 1852.  Rabenh. Krypt. Flor. Sachs. 
I: 263. 1863; Flor. Eur. Alg. 3: 365. 1868. Cooke, Brit. 
E. W. Ale 182. A. 70. f. 4. 1883. (?) Wittrock; Nordensk. 
Stud. och Forskning. A. 3. f. 27, 28. 1883. (?) 
Hormidium variabile Kütz. Phyc. Germ. 192. 1845. 
Ulothrix subtilis variabilis Kirchner, Krypt. Flor. Schles. 
2!: 77. 1878. Wolle, EW Ale 136. 27. 778. f. 15, 16.1887. (?) 
Hormiscia subtilis variabilis DeToni, Syll. Alg. 1: 160. 1889. 
Filaments forming floccose masses: cells 5-6 in diameter, 
Lj—1145 times as long, often square in optical section ; cell-wall 
very thin and delicate ; chromatophore rarely covering more than 
half the cell-wall, sometimes taking the form of a rectangular 
plate, sometimes that of an angular mass contracted into one 
corner of the cell; the pyrenoid small but distinct (ai, 27, f. 5-7). 
In brooks and in stagnant waters. 
MassacHUsETTS : Ipswich, May (557). 
New York: East Chester, May (590). 
New Jersey: Undercliff, Bergen county, April (278), May 
(369, 427 B, 574). 
It is a matter of great difficulty, if not impossible, to obtain from 
the exsiccatae any valuable evidence as to the essential character 
of such species as Ulothrix tenerrima, U. variabilis, and U. subtilis ; 
the last two we have been unable to restore from dried specimens 
