106 FRESH-WATER A L G .E OF THE U i\ 1 T E D STATES. 



P. liviiij^ on rocks and mosses, swimming in a transparent, sometimes light-green jelly; cells 

 obtusily truncated, rounded at the ends, 2-3 times longer than broad ; chlorophyl lamina 

 axillary, mostly indistinct, often wanting; endochrome light-greeu ; nucleus generally distinct; 

 zygospore subfuseous, either globose or of an irregular form, somewhat resembling that of an 

 hour-glass ; external coat irregularly excavated and sulcate. 



Remarhs. — This species was found along the North Pennsylvania Railroad, near 

 Chelten Hills, growing amid mosses on tlie rocky jiittings over which the water 

 was dripping. It occurs as a rather firm, transparent jelly, mostly of a light 

 greenish tint, in whicli the cells are often placed quite thickly. They are cylin- 

 drical, mostly straight, but sometimes slightly curved, and often completely filled 

 with a light greenish endochrome. The central lamina is irregular, and mostly 

 not at all pronounced. In some cells the endochrome is much broken up, so that 

 the interior is filled with little green masses with light spaces between them. In 

 these cells the nucleus is generally not perceptible, whilst in the others it is very 

 weU marked. The zygospore is often globular, sometimes it is irregularly elliptical, 

 with a constriction in the centre, so as to give it somewhat of an hour-glass shape. 

 The outer coat mostly fits pretty closely on the inner contents, and is very often 

 distinctly marked with little pits, some round, some irregular in shape; in otlier 

 cases, instead of being thus pitted, the spores seem to be marked with deep curved 

 furrows. 



Fig. 4, pi. 11, represents this plant in different stages of growth. (See Expla- 

 nation of Plates.) 



Genus PENIUM, Breb. (1848.) 



Cellulae cylindricse vel fusiformes, rectoe, ntroque polo rotundatoe vcl trnncato-rotundatfe (nee emar- 

 gioatie nee excisas), medio saspius constrictte. Lamina chlorophyllaceaaxilis, ex transverse conspccta 

 radiatim-divcrgens, radii scepe furcati, granula amylacca plerumque longitudinaliter seriata includens. 

 Individua in aqua libere natantia, singula, sparsa vel in massa gelatinosa consociata. Cellulae mem- 

 brana tevis vel granulata, achroa vel fuscesceus vel rubicunda, saepius longitudinaliter striata. (R.) 



Syn. — Ndriiivi, Nveqeli. 



CylindrocystLs, Mengh. 

 Closlerium, jMrlim, Ehrenberg. 



Cells cylindrical or fusiform, straight, rounded at each end, or truncately rounded (not emarginate 

 or excised), medianly often constricted. Chlorophyl lamina axillary, when seen transversely radi- 

 ately divergent, arms often forked, and containing starch granules, mostly longitudinally striate. 

 Individuals swimming free in the water, scattered and single, or associated in gelatinous masses. 

 Cell membranes smooth or granulate, transparent or fuscous or reddish, often longitudinally striate. 



a. Lamina chlorophyllacea peripherice lobala vel radiatim expansa. 

 a. Chlorophyl lamina, lobate on the periphery or radiately exjmnded. 



P.Dig;itii!!i, (Ehrb.) Breb. 



P. cellulis ovato-cylindricis, diametro 3-5 plo longioribus, utroqne polo parum attenuatis, snb- 



truncato-rotundatis ; laminis chlorophyllaceis peripherice lobatis, medio interruptis. 

 Diam.—jl^^" = .00173"— 7|§/ = .0029". 



Syn.— P. Digitus, (Ehrb.) Br£b. Rabenhorst, Flora Enrop. Algar., Sect. III. p. 118. 

 Cells ovately cylindrical, 3-5 times as long as broad, at each end slightly attenuate, snbtrun- 



cately rounded; chlorophyl lamina lobate on the periphery, interrupted in the middle. 



