FRESH -WATER ALG.E OF THE UNITED STATES. 49 



its fellow. This coating Avas not at all uniform, but was covered with mammillated 

 masses, and consequently varied from two to six lines in thickness. Internally, it 

 was striated or radiated, but not so evidently as the following species, and presented 

 several distinct variegated zones. It was quite soft to the touch, as well as readily 

 broken or crushed, and under the microscope was seen to contain very little lime 

 salt. When dried it has a pronounced sebaceous appearance. The filaments com- 

 posing it are remarkable for their great length, often apparently running from the 

 bottom to the top of the frond. They are rarely if ever branched, and appear 

 never to be furnished with any heterocysts save at their enlarged base. I have 

 never seen any distinct hairs terminating them, their ends always appearing broken 

 and open. They are often quite flexuous or even tortuous. The internal filament 

 is remarkable for having its articles so distinctly separated. It is often very much 

 interrupted, and in specimens preserved in carbolic-acid water is of an orange-brown 

 color. 



Fig. 3, pi. 4, represents a single filament magnified 260 diameters. 



Z. pnrcezonnta, Wood, (sp. nov.) 



Z. nigro-viridis, enormiter semiovalis, ad 6'' longa, dura, lubrica, non fragilis, calce prsgnans, 

 intus a basi distincte radiata, parce et saepc obsolete zonata ; trichomatibus luodice lougis, 

 subrectis; trichomatibus internis cylindricis inarticulatis vel articulatis, et interdum mouili- 

 formibus ; articulis longis et cylindricis vel brevibus et globosis ; vaginis amplis, fibrillosis ; 

 cellulis perdurantibus basalibus et integectis, Lis oblougis vel cylindricis, illis globosis et 

 ssepe gemiuis. 



Diajn.— Cell. perd. basal. 5i5Vi5"=000n"; trichom. cum vag. ju'jo"—5tf'ou"=- 00026"— .00037". 

 Sine vag. .00006"— .00008". 



Hah. — In saxis irroratis. " Cave of the Winds," Niagara. • 



Var. — Z. cinerea. 



Blackish green, irregularly semioval, to 6 lines long, hard, slippery, not fragile, impregnated with 

 lime, internally distinctly radiate, sparsely and often obsoletely zoned ; filaments moderately 

 long, straightish ; internal filament cylindrical, not articulated or articulated, sometimes monili- 

 form ; joints long and cylindrical, or short and subglobose ; sheath ample, fibrillose ; heterocysts 

 basal and interposed in the body of the filament j the former globose, often geminate ; the 

 latter oblong or cylindrical. 



Yar. — Cineritious in color. 



Remarks. — I found this plant growing on rocks as glossy, blackish, very hard and 

 slippery fronds or masses, which varied in size from that of very small shot to 

 nearly half an inch in length. The larger ones were not nearly so high as long, 

 and presented irregular, almost bossellated upper surfaces. The filaments are 

 often very evidently and frequently pseudoramose. The external surface of the 

 broad sheath is covered with numerous fibrillte, which envelop and seem sometimes 

 to wrap it round and round. The color of the frond internally, when broken, is 

 mostly a dark chocolate, and the surface presents a radiated appearance, with but 

 two or three zones at most, and, in the very dark specimens, even these are not 

 evident. No signs of spores have been found. Certain specimens which I ob- 

 tained growing with the others, instead of being blackish in color, are grayish, but 



7 April, 1872. 



