FRESH-WATER ALG^ OF THE UNITED STATES. 73 



specimens collected in the month of August, which grew on boards over which 

 spring water was constantly running. These specimens agree perfectly with the 

 others, except that the filaments are larger and the elongated apical cell is wanting; 

 differences which I believe to be due to the specimens collected in August being 

 older than those first received. 



Fig. 2 a and 2 6, pi. 9, were taken from the types, whilst fig. 2 c, pi. 9, from the 

 August specimens. 



a. Cellulae plerumque in serie duplici vel multiplici. 



a. Cells generally in double series, or multiple series. 

 S. arg^illaceus, Wood, (sp. noy.) 



S. strato tenui, expanso, subnigro, submembranaceo ; trichomatibus brevibus, dense intricatis 

 et seepe nonnihil concretis, ramosis, irregularibus ; pseudoramulis brevibus, varie curvatis, 

 nonnihil rigidis, plerumque ascendentibus, apice nonnihil attenuatis; cellulis subglobosis, 

 saepe compressis, plerumque in serie simplici sed interdum in serie duplici, vel rare multiplici ; 

 cellulis apicalibus valde elongatis, cylindricis, scytonemae trichomatibus internis similibus; 

 vaginis crassis, firmis, in trichomatibus maturis saturate rubido-brunneis, in ramulis saepe luteo- 

 brunneis et in apice hyalinis et fere coloria expertibus ; cellulis perdurantibus nullis. 



Diam.—g^^s" = .000833". 



Hab. — In palude argillacea, South Carolina. (Ravenel.) 



Stratum thin, expanded, blackish, submembranaceous; filaments short, densely intricate, and 

 frequently somewhat concreted, giving origin to numerous branches, irregular ; branches short, 

 variously curved, somewhat rigid, mostly ascending, apex somewhat attenuate; cells sub- 

 globose, often compressed, mostly in simple series, sometimes in double, rarely even in multi- 

 ple ; apical cells elongate, cylindrical, resembling the inner filament of a scytonema ; sheath 

 thick, firm, in the mature filament deep reddish-brown, in the branches yellowish-brown, at the 

 apices of the branches nearly colorless and transparent ; heterocysts absent. 



Bemarks. — I am indebted to Prof. Eavenel for this plant, which was found by 

 him on a moist clay bank near Aiken, South Carolina, August, 1869. It forms a 

 thin, somewhat membranous, dark stratum, the filaments of "which are so closely 

 united that it is almost impossible to tease them apart with needles. Neighboring 

 filaments are often united at the edges so as to form distinct bundles, and even 

 the branches are sometimes concreted, although, generally, as seen under the 

 microscope, they project from the mass in all directions. The surface of the fila- 

 ments is mostly rough and ragged with fibrillse and membranous projections. In 

 the older filaments the cells are often entirely absent. They are mostly single, 

 but sometimes multiple in the filaments ; in the branches they are often partially 

 double. The ends of the older branches are often broken and empty, whilst those 

 of the younger are rounded. The color of the cells, as I have seen it, does not 

 strikingly differ irom that of the sheaths. 



Fig. 3 a, pi. 9, represents a portion of an old frond magnified 460 diameters, 

 and fig. 3 6, the end of a younger branch. No. 79. Collection of Ravenel, Aug. 

 1869. 



S. g^uttnla, Wood. 



S. in maculis subnigris, parvis, tenuibus, plerumque rotundatis, interdum enormibns, dispositus; 

 trichomatibus arete intertextis. ramossissimis, rigidis, inaequalibus, subcylindricis, nonnihil 

 10 May, 1872. 



