46 FRESH-WATER ALGJE OP THE UNITED STATES. 



Z)iam.— Trichom. cum vag. ^h^s"—^{^s^s"■, sporis max. tbIju"— 75%?)" 5 cell. perd. j-^U^". 



Syn. — G. incrustata, Wood, Prodromus, Proc. Amer, Philos. See, 1869, p. 128. 



Hab. — Schuylkill River, plantas aquaticas adhaerens. 



Frond globose or suboval, firm, solid, about the size of a very small pea, light green, crystal 

 bearing ; filaments straight or slightly curved, produced into long hairs, green or yellowish, 

 sometimes bright green in their proximal portions but yellowish above, not regularly articu- 

 late; lower articles in the mature filament short, and generally compressed; apical seta 

 straight or slightly curved, mostly indistinctly articulate, frequently interrupted; sheath 

 ample, transparent, saccate, sometimes strongly constricted; spores cylindrical, frequently 

 curved, about 9 times as long as broad. 



Bemarks. — I found this species growing attached to some little plants, either in 

 the Schuylkill near Spring Mills, or else in the spring itself, I do not know which. 

 The roundish fronds varied in size from a mustard-seed to that of a half-grown 

 pea. They were of a decided green color, but appeared grayish from the amount 

 of carbonate of lime in and upon them. The larger balls, when cut in two, were 

 distinctly separable into a central and cortical part. The former was more gela- 

 tinous and contained fewer of the filaments than the latter. The filaments mostly 

 arose in sets together, i. e. there were one or more zones or planes in which the 

 bases of the filaments were placed together. This, however, was not strictly the 

 case, as there were almost always some scattered trichomata. The matured fila- 

 ments are very distinct. Their sheaths are very large, and often saccate, with 

 wavy, loose-looking margins ; sometimes they are suddenly transversely constricted, 

 once or more in their length ; sometimes they look as if a tight spiral band were 

 vpound around ; sometimes they are entirely free from any constrictions. These 

 sheaths are open above, appearing as though they had been melted away. The 

 spore is long and cylindrical, and is highly granular. The endochrome is gene- 

 rally articulated below, the joints are often so nearly globular in the lower portions 

 as to give a moniliform appearance; sometimes the articles are compressed. The 

 upper portion of the trichoma is frequently interrupted, and if at all articulated 

 is very irregularly and indistinctly so. The younger filaments have their endo- 

 chrome variously and irregularly interrupted. The basal cells are globular. I 

 believe the formation of new filaments and the consequent growth of the frond 

 take place by distal portions of the projecting endochrome separating from the 

 parent filament, then forming a basal cell, and lastly a sheath. (See Plate 00.) 

 The carbonate of lime does not exist as a definite incrustation, but in the form of 

 semi-crystalline masses scattered through the frond. This species seems to come 

 closer to G. horyana than any described species, from the description of which it 

 differs, in the color of thallus, in the latter being always solid (at least so I have 

 found it late in the fall, when the spores were fully perfected), in its habit of in- 

 closing crystals of carbonate of lime, in the curved spores; and, doubtless, a com- 

 parison of the specimens would show still more important differences. 



Fig. 4 a, pi. 3, represents a section of a frond moderately magnified ; fig. 4 h, 

 the basal end of a filament magnified 460 diameters ; fig. 8 c, filaments magnified 

 260 diameters. 



