80 FRESH- WATER ALG.E OF THE UNITED STATES. 



Zttoro. Cell, glob. max. ^ v " = .00028"; cell, oblong, long. max. 35 Vs" = .0004". 



Syn. P. Jesenii, WOOD, Prodromus, Proc. Am. Philos. Soe., 1869, p. 134. 



Hub. In rupibus irroratis, prope Philadelphia. 



Thallus indefinitely expanded, in the beginning soft and pellucid, afterwards firm, tubercular, 

 deep olive-green ; cells globose or elliptical ; in the immature thallus, single or geminate, fre- 

 quently scattered ; in the mature thallus often closely conjoined into families, mostly crowded ; 

 in the young thallus the teguments of the cells are mostly diffluent, afterwards distinct. 



Remarks. This little plant was found along the banks of the Schuylkill River, 

 just above Flat Rock tunnel, near Manayunk, forming in the early winter a gela- 

 tinous mass of two to three lines in thickness, irregularly and. interruptedly spread 

 over the face of wet, dripping rocks. In what appeared to be the younger por- 

 tions, the jelly was often quite soft and almost colorless, and had the cells scat- 

 tered rather sparsely and distantly through it. The cells were but partially filled 

 with chlorophyl, the vacuole left containing often numerous granules, and had 

 distinct walls, being, as it were, merely immersed in the general maternal jelly. 

 In the older fronds the texture is more firm, the color a deep green, and the bright 

 green cells are mostly surrounded by a thick, very distinct tegument. They are 

 also largely arranged in little families of two, four, or even eight cells, surrounded 

 by a common integument. The oldest fronds are of a deep olive, almost blackish 

 color, markedly tuberculate upon their upper surface and very firm in texture. 

 They are surrounded by very distinct, firm, dark brown coats (a simple coat often 

 involving two or more cells), and arranged in groups or families. As shown by 

 the microscope in the superficial portion of such fronds, the jelly is of a yellowish- 

 fuscous color, and the cells are themselves of a dark brown tint. The number of 

 cells in the individual families varies from two to a dozen or more. Even in these 

 old, firm fronds, the interior portions are frequently composed of greenish cells, 

 without any distinct teguments or coat. In such cases the cells are mostly oblong 

 or elliptical, and very much crowded together. This species appears to come 

 closest to P. BrSbissonii, KTZ., from which it differs, however, in its habit of 

 growth and the size of its cells. 



Fig. 3 a, pi. 10, represents a fragment of the upper surface of an old frond 

 magnified 750 diameters; fig. 3 b, when taken from the inner jelly of similar 

 fronds. 



P. dura, WOOD, (sp. nov.) 



P. thallo enormiter subgloboso, enormiter minute lobato vel verrncoso, caeruleo-nigro, nonnihil 

 crustaceo, minuto ; cellnlis arctissime coufertis, plerumque enormiter oblongis, ssepe in serie- 

 bus irregulare dispositis, cseruleo-viridibus vel luteo-brunneis ; tegumentis baud distinctis ; 

 sporis globosis vel ovalibus. 



Diem. Cell. nW'-.OOOOS"^"- .00016"; spor. T5 ^ 5 " = .00058" 75 <W' = . 0008" 

 Hob. In fonte prope Philadelphia. 



Thallus irregularly snbglobose, irregularly minutely lobate or warty, bluish-black, somewhat 

 crustaceous, minute ; cells densely crowded, mostly irregularly oblong, often arranged irre- 

 gularly in series, bluish-green or yellowish-brown ; coats not apparent; spores globose or 

 oval. 



