ULOTHRIX 149 
cient to convince one of their relation, as young forms, to this 
largest species of the genus. 
In May the rocky borders of the lake in Central Park become 
fringed with a growth which rapidly develops into the typical 
U. zonata. We have never found this growth early in the season, 
and it disappears soon after the first hot days at the end of May 
or in June. 
A number of species and varieties of European authors have 
not been satisfactorily distinguished as more than growth forms of 
U. sonata. Such are U. pectinalis Kütz., U. inaegulis Kütz., 
U. zonata attenuata (Kütz.) Rabenh., U. zonata varıans (Kütz.) 
Rabenh., U. sonata valida (Nàg.) Rabenh., and U. sonata rigidula 
(Kütz.) Hansg. 
2. ULOTHRIX TENUISSIMA Kitz. Flora, 16: 518. 1833; Phyc. 
Gen. 252. 7 
Ulothrix tenuis Kitz. Phyc. Germ. 197. 1845; Spec. Alg. 
347. 1849 (Not U. tenuis, ıbid., 346); Tab. Phyc. 2: pl. 89. 
f. r. 1852. Rabenh. Flor. Eur. Alg. 3: 366. 1868. Cooke, 
Brit. F. W. Alg. 182. A. 70. f. 6. 1883. Wolle, F. W. Alg. 
$44. A TO, 22 1887, 
Myxonema tenuissimum  Rabenh. Deutsch. Krypt. Flor. 2: 
99. 1847. 
Hormiscia tenuis De Toni, Syll. Alg. 1: 165. 1889. Hansg. 
Prod. Alg. Bohm. 2: 213. 1892. 
Dark green; vegetative cells always thin-walled, 15-204 
(rarely 25 (م‎ in diameter in mature filaments, generally about half 
as long or shorter, sometimes in younger filaments as long as the 
diameter, cylindrical, not at all constricted at the septations ; chro- 
matophore broad; zoösporiferous filaments somewhat moniliform 
(AL 20. f. 5, 6). 
In running water in brooks and watering troughs. 
New York: Central Park, April (265, 535), May (380). 
New Jersey: Fairview, April (297). 
Numerous specimens that were at first referred to this species, 
have been proved, after subsequent collection in the same stations, 
* Kützing abandoned this name first given to the species without any expressed 
reason, but probably because he felt that it was not properly descriptive of the plant 
after he added to the genus several species that were smaller in respect to diameter, 
