60 FRESH-WATER ALG^E OF THE UNITED STATES. 



their stems and branches. These mats never exceeded an inch in length in any 

 specimens that came under my notice. The filaments themselves are apparently 

 not much branched and are densely interwoven. The sheaths are close, rather 

 thick, not lamellate, of uniform diameter, except in that they are occasionally 

 locally swollen, and are truncate and open at the end. The internal filaments are 

 frequently much interrupted, and in the younger plants are of a deep green. The 

 joints are in many instances much separated, and in most cases very distinct. 

 The filaments, indeed show a remarkable tendency to break up at the joints, so as 

 to form a series of dish-like gonidia, so that the articles, or endochrome masses, 

 may be generally described as strongly compressed spheres. In all the specimens 

 that I have examined, I have seen but a single heterocyst. This was at the base 

 of a branch, was somewhat reniform, and about three-fifths as long as broad. I 

 have referred this species, doubtfully, to S. Naegelii, Ktz., the only account of 

 which that I have met with, or know of, is a brief diagnosis in Rabenhorst's Flora, 

 in which many of the essential characters are omitted. 



Fig. 6, pi. 8, represents a portion of a filament of this species. 



S. thermale, KTZ. 



S. strato tenne, nigrescente ; trichomatibus flexuoso-curvatis, intricatis, parce pseudoramosis, 

 internis pallide aerugineis, saepe coloris fere expertibus, passim interruptis, plerumque inar- 

 ticulatis sed saepe indistincte et interdum distincte articulatis, granulosis ; articulis dianict.ro 

 brevioribus vel subaequalibus ; pseudoramulis plerumque brevibus, geminis, in diametro tri- 

 chomatibus aequalibus vel subaequalibus et interdum usque ad medium conjunctis, basi coa- 

 litis, saepe e basi divergentibus; vaginis crassis, indistincte lamellosis, vel luteo-fuscis vel 

 fuscis, sed passim fere coloris expertibus, plerumque vix pellucidulis, in ramulorum apice 

 saepe hyalinis et coloris fere expertibus ; cellulis perdurantibus, subquadratis vel cylindricis, 

 singulis, interjeetis. 



Diam.Tr. cum vag. jug" riW = .00042" .00058; sine vag. ,^"=.000166" 

 V = - 00025. 



Syn. S thermale, KTZ., RABENHORST, Flora Europ. Algarum, Sect II. p. 250. 

 Hab. In terra argillacea, South Carolina. (Ravenel.) 



Stratum thin, blackish; filaments flexuously curved, intricate, sparingly branched; internal 

 filament pale-greenish, often almost colorless, here and there interrupted, mostly inarticulate, 

 but often indistinctly and sometimes distinctly articulate, granular ; joints shorter or about as 

 long as broad ; branches geminate, mostly short, equal or snbequal to the filament in diameter, 

 coalescent at the bases, rarely so even to their middle, mostly divergent from the base ; sheath 

 thick, indistinctly lamellate, yellowish-fuscous, and scarcely semitransparent, but here and 

 there nearly colorless and pellucid, generally so in the apices of the branches; heterocysts 

 subquadrate or cylindrical, single, interspersed. 



Remarks. I am indebted to Professor Ravenel for specimens of this species pro- 

 served in solution of acetate of alumina. The label reads, "Damp surface of hard 

 clay, Sept. 25, 1869." The sheaths are quite thick and scarcely translucent, so that 

 the color of the inner filament seen through them is that of themselves. Curiously 

 enough, one of these dark sheaths will for a space lose its color and be very trans- 

 parent, in such places and in the apices of the branches, the inner filament is often 

 a decided pale-green ; at other times it is almost colorless. The end of the sheaths 

 are mostly closed, but I have seen them open, with the inner filament project- 



