214 FRESH-WATER ALG^ OF THE UNITED STATES. 



cells, which dissolve into oblong, oval, transparent immotile spermato- 

 zoids [Sporidia Ag.). 



2. Cystocarpia Ktz., or PistilUdia, formed of somewhat moniliform son, 

 which are evolved from a generally cortical placenta, and are naked or 

 surrounded by a mucilaginous cuticle or involucre, and finally emit 

 numerous immotile spores {polyspores), which quickly germinate. The 

 fecundation of the cystocarpia occurs in their primordial state by con- 

 tact of the spermatia with a piliform organ known as trichogonia. 



3. Tetrasporangia formed of single, greatly swollen cortical cells, be- 

 coming cruciately quadrilocular by division of the primordial utricle ; in 

 each loculus {secundary or sister cells) a single spore itetraspore) forms, 

 which germinates without fecundation. 



Family PORPHYRACE^. 



Thallus mucoso-membranaceus, foliaceus vel filamentosus, e cellularum seriebus vel strato nnico 

 formatns, plerumque purpurascens, valde lubricus. 



Vegetatio fit cellularum diTisione in duas vel omnes directiones repetita. 



Propagatio fit tetrasporis. Cystocarpia nondum observata. 



Thallus mucous-membranous, foliaceous or filamentous, formed of cells in series or in a single stra- 

 tum, mostly purplish, very slippery. 



Growth taking place by repeated division of the cells in two or all directions. 



Propagation by means of tetraspores. Cystocarps not yet observed. 



Remarks. — The only species of this family as yet observed in North America 

 can hardly be said to have a definite thallus. They are rather multitudes of cells 

 heaped together and closely attached to one another into a shapeless expanded 

 mass. 



Genus POEPHRYDIUM, Naec. rl849). 



Thallus mucoso-membranaceus, subcrustaceus, longe lateque expansus, e cellulis globosis vel 

 polyedricis compositus. Propagatio adhuc ignota. 



Thallus mucous-membranous, subcrnstaceous, long and widely expanded, composed of globose or 

 polyhedral cells. Propagation unknown. 



P. crneGitiim, (Ag.) Naeg. 



P. thallo saturate purpuro-sanguineo, lubrico ; cellulis anguloso-rotundatis. (R.) 

 Dmm.— 0.00027"— 0.00035". (R.) 

 Eab. — New York. 



Syn. — P. cruentum, (Agard.) Naegel. Rabenhorst, Flora Europ. Algarum Sect III 

 p. 397. 



- Thallus deep crimson purple, slippery ; cells angled and rounded. 



Bemarhs.—Th.e only specimen I have seen of this species was a little speck, 

 adherent to a bone picked up on Governor's Island, in New York Harbor. It is 

 very probable that it was a recent arrival, brought over, perchance, by some emi- 

 grant. For it I am indebted to Dr. Billings, U. S. A. The description and 



