FRESH-WATER ALG^ OP THE UNITED STATES. 61 



ing. The branches are nearly always short, and divergent from their united bases. 

 The heterocysts have frequently one of their ends rounded; and are quite 

 numerous. This species corresponds too closely to Rabenhorst's description of 

 Sci/tonema thermale to be separated, but it is possible a comparison of specimens 

 might show decided differences— the description of the European form is not very 

 full. The American plants seem to approximate most closely the Var. intextum. 

 I have seen a single branch given off only in one instance. 



Fig. 1, pi. 6, represents a filament of this species magnified 260 diameters.; fig. 

 1 &, the outline of a heterocyst magnified 750 diameters. 



S. Hyochrous, Ag. 



S. strato tenui, pannoso-tomentoso, obscure fusco (nonnunquam subsericeo) ; trichomatibus 

 validissimis, fuscis, lucidis, leniter curvatis, adscendentibus, internis serugineis, apice (articul. 

 term. 5-6) rubellis, distincte articulatis ; pseudoramulis plerumque geminis, ssepe longissimis 

 flaceldo-erectis, trichomate dimidio circiter tenuoribus; trichomatis vaginis crassis, distincte 

 lamellosis, firmis, pulchre luteo-fuscis, superficie laevissimis, ramulorum semper pallidioribus 

 (luteis, rarius achrois), apice ssepe achrois, clausis et obtuso-rotundatis ; cellnlis perdu- 

 rantibus oblongis vel subcylindricis, achrois, trichomatis interni diametro snbfequalibns. 

 (R.) Strato obscure olivaceo, trichomatibus parce pseudoramosis, ad -^j" crassis ; pseudo- 

 rannulis singulis, vaginis achrois vel luteolis ; vag. tricb. luteo-fuscis. (R.) Species mihi 

 ignota. 



Diam—Trichom 0.0011"— 0.0014"; ramulorum ad 0.00068". (R.) 



Syn. — S. Myochrous, Agardh ; Var. Gontextum, Cabmichael. Rabenhorst, Flora Europ. 

 Algarum, Sect. II. p. 254. 



Hob. — " Foot of Crow's-nest,. West Point." Bailey. Silliman's Journal, N. S. vol, iii. 



Strato thin, pannosely tomentose, obscurely fuscous (sometimes somewhat silky) ; filaments very- 

 strong, fuscous, bright, slightly curved, ascending ; the internal seruginous, distinctly articu- 

 late with the apex (terminal 5-6 joints) reddish ; branches mostly geminate, often very long, 

 flaccidly erect, about one-half thinner than the filament; sheath of the filament thick, dis- 

 tinctly lamellate, firm, beautifully yellowish-fuscous, surface very smooth ; sheath of the 

 branches always paler (luteous or rarely colorless) with the apex colorless, short and obtusely 

 rounded ; heterocysts about equal in diameter to the internal filament. Stratum obscurely 

 olivaceous, filaments sparsely branched, about ^y" thick ; branches single, with the sheaths 

 transparent or yellowish ; sheath of the trichoma luteo-fuscous. 



S. calof richoides. Kutzing(?). 



S. caespitosum, raucosum, plerumque cum algis variis intermixtum; trichomatibus plus minus 

 curvatis; pseudoramulis plerumque geminis, varie curvatis, simplicibus, elongatis; tricho- 

 matibus internis modo distincte articulatis, modo inarticulatis, interdum moniliformibus, 

 luteo-viridibus vel aerugineis, granulosis ; articulis plerumque diametro brevioribus sed in- 

 terdum permulto longioribus, baud rare vel subglobosis vel valde compressis ; cellnlis per- 

 durantibus singulis, subcylindricis; vaginis plerumque peliucidulis, distincte lamellosis, in 

 trichomatibus plerumque rubido-vel luteobrunneis sed interdum colons expertibus, in pseu- 

 doramulis hyalinis, coloris expertibus vel dilutissime luteis vel dilute luteo-brunneis. 



Diam— Cum vag. max. 55^5/'=. 00075"; plerumque 5^%/ =-00045"; sine vag. 75^x7' — 5T>W; 



pseudoram. ^^^tj" = -0005". 

 Syn.—S. calotrichoides, Ktz. Rabenhorst, Flora Europ. Algarum, Sect. II. p. 252. 

 Hab. — South Carolina. (Ravenel.) 



