2U FRESH-WATER ALG^ OF THE UNITED STATES. 



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

 zoids {Sporidia Ag.). 



2. Cystocmyia Ktz., or PistilUdia, formed of somewhat moniliform sori, 

 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 tricJiogonia. 



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 [fetrasjwrc) forms, 

 which germinates without fecundation. 



K^MiLY PORPHYRACE^. 



Thallus mucoso-merabranaceus, foliaceus vel fSlamcntosus, e cellularuni soriebus vel strato unico 

 formatiis, ])lenimquc purpurasceus, valde lubriciis. 



Vegetatio fit cellularum divisione in duas vel omnes directiones repetita. 



Propagatio fit tetrasporis. Cystocarpia noudum observata. 



Tliallus mucous-membranous, foliaceous or filamentous, formed of cells in scries 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 

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

 mass. 



Genus PORPHRYDIUM, Naeg. a849). 



Thallus mucoso-merabranaceus, suberustaeeus, longo lateque expansus, e cellulis globosis vel 

 polyedricis compositus. Propagatio adliuc ignota. 



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

 polyhedral cells. Propagation unknown. 



P. criicBilnin, (Ag.) Naeq. 



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

 Diaw.— 0.00027"— 0.00035". (R.) 

 . Hah. — New York. 



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

 p. 397. 



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



Remarls. — The only specimen I have seen of this species was a little spock, 

 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 



