182 FRESH-WATER ALG^ OF THE UNITED STATES. 



Multicellular, chlorophyllous algae, membranaceous or filamentous, furnished with or destitute of 

 branches. Propagated by oospores or zoospores, never by conjugation. 



Family ULVAOE^. 



Thallus membranaceus vel foliaceus, vel filiformis (Schizomeris?) rarins crustaceus, e cellularum 

 strato unico formatus, aut expansus aut tubuloso- vel vesiculoso-concretus. 



Propogatio fit zoogonidiis, cytioplasmatis divisione repetita ortis. Zoogonidia oblouga, polo 

 antico ciliis vel binis vel ternis vel quarternis instructa. 



Thallus membranous or foliaceons, rarely crustaceous, composed of a single stratum of cells, either 

 expanded or tubularly or vesicularly concreted. 



Propagation by means of zoogonidia, formed by the repeated division of the cytioplasm. Zoogoni- 

 dia oblong, furnished with two, three, or four cilia at the anterior end. 



Genus PEOTODEEMA, Ktz. 



Thallus crustaceus, indeterminatus, substrato arete adhaerens, e cellulis anguloso-rotundatis, 

 irregulariter ordinatis, arete connexis compositus. 



Propagatio ignota. 



Thallus crustaceous, indeterminate, closely adherent to the substratum, composed of closely con- 

 joined irregularly arranged angularly rounded cells. 



Propagation unknown. 



P. Tiride, Ktz. 



P. viride, lubricnm. 



Syn. — P. viride, Ktjtzing. Rabenhorst, Flora Europ. Algarum, Sect. III. p. SOT. 



Hah. — In aquario; Wood. 



Green; slippery. 



Remark. — I have seen a plant, which I take to be this species, growing on the 

 glass and on pebbles in the aquarium of my friend. Dr. Fricke. 



Genus ULVA, Linn. 



Thallus membranaceus, plane expansus, angustus vel latus, nonnunquam latissimus, magis minusve 

 undulato- crispatus, ssepe laciniatus, hand raro perforatus, e cellularum strato unico formatus, callo 

 disciformi parvo af&xus, aetate provecta ssepe libere natans. Cellulte anguloso-rotundatse, cceloplas 

 maticsB, parenchymatice connexae. 



Vegetatio cellularum divisione in duas directiones repetitia. Propogatio fit zoogonidiis, in cel- 

 lulis quibnsdam cytioplasmatis divisione 4, 8-16 ortis, ciliis vibratoriis quaternis longitudine cor- 

 poris longitudinem vix superantibus instructis. 



Thallus membranous, expanded, narrow or broad, sometimes very broad, more or less undulately 

 curled or crisped, often laciniate, not rarely perforate, formed of a single stratum of cells, fastened 

 by a small discoid thickened portion, in advanced age often swimming free. Cells angularly glo- 

 bose, joined into a sort of parenchyma. 



Growth occurring by the repeated division of the cells in two directions. Propagation by 

 zoospores, 4-8-16 of which are formed at once by a division of the endochrome of certain cells, 

 and are furnished with four vibratile cilia scarcely longer than the body, 



U. merismopedioides, Wood. 



TI. ampla, membranacea, late expansa, dilute viridis, tenuis, radiatira et enormiter plicata, ambitu 

 saspe subrotundata; margine undulato, interdum subcrenato ; cellulis enormiter ovalibus vel 

 angularibus, nucleo destitutis, quarternariis et in familias Merismopediarum modo obscure 



associatis. 



Diam.— Cell max, j^^j,^" = .00041', plerumque ts^tto" — TTr^TTo" = .00016' — .00025. 



