r.BBSB-WATIB ALQ.E OF Till: r N I T K D STATES. 15 



The frond is \ { -r\ sharply <1< lim d, and, uutlrr a !<>\v pm\er. i- nf a uniform bluish- 

 M tint. The celK an- a--neiated in primary families of lii.nl' a number of . 

 which the thallu* k composed. The species appears to be most closely allied to 

 M. nniliti //(//<*, Na u' . tVuiii whirh it ditiers \ery I'ssrntiully in tin- M/e of the fronds, 

 and perhaps even more closely to M. ylnnm. tbe only character .separating it from 

 which is the straight margin. 1 have m\self some doubts whether it ought not to 

 he considered as merely a I'onji of M. ijluiu-n. 



Fig. 8, pi. s, represents this sp, ., -i, - s , magnified 400 diameters. 



JTI. ronrolutn, I!ur.n. 



M. tluillo ini'inliranacco, oculis nudis visiKili, plus minus convoluto; faniillis c celluli-< ^nninis ct 

 in Milifamilms i|i~|^'-;!i-, J.'ii'i oniipositis, inti-nluia familiis cluabus in familia gi'ininu CUIIJUDC- 

 tis; ct-llulis .-pli;i-rici.s aut obluiigis; cytioplosmate homogcnco, viridi. 



Diam. Cell. /" = 0.00017"; fam. long. ,!" - .06"; lat t fa" - 0.04". 



//,//, In acpiis quietis propc Philadelphia. 



Tlmllus mriiilirnniiiis, visible to tho naked eye, more or less folded; families composed of 250 

 p'Miinntf crlls, arranp'il in siilifainilios, sometimes two of these families conjoined with a com- 

 posite family ; cells spherical or oblong; cytioplasm homogeneous, green. 



/,'< murk*. "When my Prodromus was published, the only specimens of this plant 

 which I had seen were contained in a mounted slide given me by my friend Dr. J. 

 (iibboiis Hunt, of this city. Since then I have found it growing in a very shallow, 

 quiet, but fresh, sweet pool at Spring Mills, making a distinct green layer upon the 

 mud many feet in extent. Of course, there were millions of specimens in this layer. 

 The fronds are irregular in shape, often somewhat ovate, sometimes subquadrate, 

 varioush torn, and not rarely somewhat lobate. Their edges are frequently very 

 sharply defined and rendered firm and prominent by several rows of cells being 

 en iwded closely together along them. The cells in the body of the frond are arranged 

 in larijr parallelogrammatic families, composed of 256 cells. There are 16 cells on 

 cadi sidc% the- families being parallelogrammatic rather than square, owing to the 

 oblong shape of the cells. This cell family is composed of four subfamilies, each 

 containing <!4 celK These arc again subdivisible into four more or less distinct 

 groups of 16 cells each. The cells are, finally, generally closely geminate, each 

 pair being very distinctly separated from its neighbors. In certain stages of growth, 

 as immediately after a general division of the cells, two of the large cell-families 

 spoken of are often temporarily joined together to form a huge family of 512 cells, 

 but soon separate one from the other. 



ORDER Nematogeiieas 



Plant multicellnlarcB vel pscudo-mnlticellnlares. Ccllulic filnm (trichoma) formantes et pic- 

 rnmque vagina tubulosa horaogenea vcl lamellosa inclusw. Trichomata aut simplicia aut ramiflcata. 



Plants multicellular or psendo-mnlticellalar. Cells forming a filament, nnd generally included in 

 a tubular lamellate or homogeneous sheath. Filaments either simple or branched. 



