FRESH-WATER A L G J3 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 liabenhorst's description of 

 Scytoaema 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 h, the outline of a heterocyst magnified 750 diameters. 



S. lUyocliroii)!), Aa. 



S. strato tenui, pannoso-tomentoso, obscure fusco (nonnunf|nani siibsericeo) ; trichoniatibus 

 validissimis, fuscis, lucidis, leniter curvatis, adscetiflentibus, internis lErugineis, apice (articul. 

 term. 5-6) rubellis, distiucte articulatis; pseudoraraulis plerumque geminis, sa;pe longissirais 

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

 lamellosis, firmis, pulchre luteo-fuscis, supcrficio l«vissimis, ramulorum semper pallidioribus 

 (luteis, rarius aclirois), apice s»pc achrois, clausis et obtuso-rotundatis; cellulis perdu- 

 rantibus obloiigis vel subcyliiidricis, achrois, trichomatis interni diametro subiequalibus. 

 (R.) Strato-obscure olivaceo, trichoraatibus parce pseudoramosis, ad ^L"' crassis; pseiido- 

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

 ignota. 



Z)m?)i.— Trichom 0.0011"— 0.0014" ; ramulorum ad 0.000G8". (R.) 



Syn. — S. Mijochrous, Agardii ; Yar. Contextum, Carmichael. Rabenhokst, Flora Europ. 

 Algarum, Sect. II. p. 254. 



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



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

 strong, fuscous, bright, slightly curved, ascending; the internal [cruginous, distinctly arliru- 

 late with the ape.x (terminal 5-G 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 ^^"' thick ; branches single, with the sheaths 

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



S. caloti*ichoide)!i. Kutzing(?). 



S. cajspitosum, mucosum, plerumque cum algis variis interraixtum ; trichoniatibus plus minus 

 curvatis; pscudoramulis plerumque geminis, varie curvatis, siraplicibus, elongatis ; tricho- 

 niatibus internis modo distincte articulatis, modo inartieulatis, inlerdum moniliformibus, 

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

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

 durantibus .singulis, subcylindricis; vaginis plerumque pellucidulis, di.«tincte lamellosis, in 

 trichoniatibus plerumque rubido-vel luteo brunneis sed interdum eoloris expcrtibus, in pscu- 

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



Z>iam.— Cum vag. max. ,^-\,^"=. 00015"; plerumque 55%/ =.00045"; sine vag. tsVt" — ?o'us"; 



pseudoram. ^^^ly" = -0005". 

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

 Hab. — South Carolina. (Ravenel.) 



