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



I have also received from Prof. Ravenel specimens of a Tetraspora, which may 

 be the young of a variety of this species, but which is very possibly distinct. If 

 the specimens are adult, it certainly is. They consist of numerous little fronds not 

 more than a third of an inch in length, often composed of several subcylindrical 

 arms, as it were, radiating from a central portion, and attaining a length of a third 

 of an inch or so. These fronds are irregularly perforate, and are composed of 

 cells agreeing perfectly in form, size, and arrangement with the more ordinary 

 forms of T. lubrica. 



T. foiillosa, (ROTH) Aa. 



T. thallo membranaceo-saccato, obovato, sinuoso-bulloso, unciam usque palmam longo, postea 

 explanato, dilacerato, saturate viridi, plus minus verrucoso; cellulis subsphericis (post divi- 

 sionem factam hemisphaericis vel angulosis) geminis vel quateruis, confertis, granulosis. 

 (R.) Species mihi ignota. 



Diam. Cell, ante divis. 0.00032" 0.00049" ; post divis. 0.00022" 0.00029". (R.) 

 Syn. T. bttllosa, (ROTH) Aa. RABENHORST, Flora Europ. Algarura, Sect. III. p. 39. 



Hub. " Salem, North Carolina. Schweinitz, Newburgh, New York." Bailey, Silliman's 

 Journal, New Series, vol. iii. 



Thallns membranaceons saccate, obovate, sinuosely-bullose, from one to six inches in length, 

 afterwards expanded, torn, deep green, more or less verrucose ; cells subspherical (after divi- 

 sion hemispherical or angular) in twos or fours, crowded, granular. 



Genus DICTYOSPH^EEIUM, N.EG. 



Thallus gelatinosus plus minus liquidns, libere natans, saepe quasi nullus. Cellulse vesicula chlo- 

 rophyllosa unica et locello achroo parietali praeditse, tegumentis crassis in gelatinam homogeneam 

 confluentibus involutae, filis propriis subtilibus dichotome diyisis, e familiarum centro ad peripheriam 

 radiantibus connexae. Cellularum divisio ad omnes directiones. 



Propagatio fit gonidiis mobilibus 



Thallus gelatinous, more or less liquid, swimming free, often almost wanting. Cells furnished 

 with a single chlorophyllous vesicle and a lateral transparent spot, surrounded with thick coats, 

 which are confluent into a homogeneous jelly and united by very fine filaments, which are dichoto- 

 mously divided and radiate from the centre to the peripheral families. Division of the cells occur- 

 ring in all directions. 



Propagation by motile gonidia. 



D. pulchelluin, WOOD, (sp. nov.) 



D. thallo subgloboso vel subovale, interdum subnullo, interdum indistincte lobato ; cellulis 

 globosis plerumque sparsis sed interdum nonnihil confertis. 



Diam. Cell. ^ v " = 0.00025" ; thalle plerumque 3 / = 0.0033" ; interdum T s " = 0.0054." 

 Hob. In stagnis prope Philadelphia. 



Thallus subglobose or suboval, sometimes indistinctly lobate, sometimes almost wanting; cells 

 globose, mostly scattered, but sometimes rather crowded. 



Remarks. I found this little plant, one August day, floating, in company with 

 Closterium acerosum, in a brick-pond below the city. The little fronds are mostly 

 roundish, or longer than broad, with a distinct outline, sometimes, however, the con- 

 stituent jelly seems to fade into the surrounding water. There is never a distinct 



