50 FRESH-WATER ALGJK OF THE UNITED STATES. 



agree in all other respects with their fellows. This gray color depends, I believe, 

 upon the deposit of an immense quantity of lime salts, which in such specimens 

 constitute by far the larger portion of the frond. 



Fig. 4, pi. 4, represents a section of frond, slightly magnified. 



It is either this, or the preceding species, which is referred to by Professor 

 Bailey in Silliman's Journal, vol. iii, under the name of Rivularia calcarea, Sm. 

 The present form may possibly be that plant, but not having been able to find any 

 description sufficiently well made out to make identification possible, I have de- 

 scribed both species as new. 



Z ininntiila, WOOD, (sp. nov.) 



Z. minutissima, nigro-viridis, subglobosa, baud distincte zonata, nonnihil mollis, muscicola, calce 

 non pragnans; trichomatibus internis, breve articulatis, distinctissime fasciculatim pseudora- 

 mosis; vaginis crassis, arnplis, ssepe dilute aurautiaco-brunneis, apice plerumque coloris 

 expertibus fissis et apertis; eellulis perdurantibus ovato-globosis. 



Diam. Trich. intern. .00012" .00021" ; cell. perd. .00025." 



Hob. In lacu, " Clear Pond," muscis affixa, Adirondack Mountains. 



Very small, blackish-green, subglobose, not distinctly zoned, rather soft, growing on mosses, not 

 impregnated with lime ; internal filaments shortly articulate, very distinctly fasciculately pseu- 

 doramose ; sheaths thick, ample, often pale orange-brown, with their apices mostly colorless, 

 torn and open ; heterocysts ovately globose. 



Remarks. The locality in which I found this plant is in the heart pf the Adi- 

 rondack wilderness. The little frond in none of my specimens is larger than a 

 mustard-seed, and is not distinctly zoned. The plants were collected in the begin- 

 ning of July, and very possibly are not fully grown, as the season of general growth 

 opens very late in its parent lake. Very possibly, later in the year, it may be found 

 larger and distinctly zoned. The general appearance of the plant, the character 

 of its sheath, and the marked branching habit of the filaments have caused me to 



place it in this genus. 



- 



Genus DASYACTIS, KTZ. 



Thallus gelatinosns. mollis, non zonatus. Trichomata matura ssepe hand vaginata. Sporae 

 nullse. 



Thallus gelatinous, soft, homogeneous, not zoned. Mature filaments often not vaginate. Spores 

 absent. 



1 mollis, WOOD. 



D. parva, ad magnitudinem pisi minimi, enormiter subglobosa, mollis, gelatinosa, dilute viridis; 

 trichomatibus plerumque subrectis, partirn distincte, partim indistincte articulatis; vaginis, 

 in trichomatibus maturis hand visibilibus, in trichomatibus juvenibus supra subamplis; cel- 

 lulis perdurantibus sub-globosis, globosis, vel ellipticis, diametro duplo majoribus, plerumque 

 singulis sed interdum bi vel triseriatis. 



Diam. Trich. M' ^ v "; cell. perd. n \ rs ". 



Syn.D. mollis, WOOD, Prodromus, Proc. Amer. Philos. Soc., 1869, p. 128. 



Hob. In palude plantas aquaticas adhaerens, Northern Michigan. 



