THE GREEN ALGAE OF NORTH AMERICA 217 



PROTODERMA Kiitzing, 1843, p. 295. 



Frond a minute disk, closely attached to the substratum, 

 formed originally of radiating, branching filaments, which, ex- 

 cept at the margin, are united to a sub-parenchymatous layer of 

 one or more cells in thickness ; cells with parietal disk-shaped 

 chromatophore and one pyrenoid ; asexual reproduction by 

 aplanospores and by biciliate zoospores with red stigma. 



The proper position of this genus is quite uncertain ; West, 

 1904, places it in the Pleurococcaceae ; Oltmans, 1904, ignores 

 it ; it must be placed somewhere, and in the Ulvaceae is as 

 good a place as any. There is no doubt that immature organ- 

 isms of many kinds have passed under the name of P. viride, 

 but P. marinum is more distinct. 



KEY TO THE; SPECIES OF PROTODERMA. 



i. Fresh water. i. P. viride. 



i. Marine. 2. P. marinum. 



^ i. P. VIRIDE Kiitzing, 1843, p. 295 ; 1856, p. 6, PI. XI, fig. i. 

 Frond pale green, at first circular, later more or less irregular; 

 filaments parenchymatously united in the interior of the disk, 

 free at the margin ; cells in the young frond with thin wall, 

 cylindric to cuneate, 3-6 p. wide, usually 2-3 times as long ; 

 in middle of adult frond 6-8, or even 12 /x. wide, 1-2 times as 

 long, spherical, ovoid, or ellipsoid, with thick wall ; zoospores 

 globose to ovoid, 3-3.5 p diam. ; aplanospores globose to ellip- 

 soid, 2-3 fj. diam. Fig. 73. On wood and stones in ponds. 

 Mass., Barbados. Europe. 



' 2. P. MARINUM Reinke, 1889, p. Si ; P. B.-A., No. LJII. 

 Forming thin coatings of irregular form, composed of angular, 

 parenchymatously united cells, 6-12 p. wide, irregularly placed, 

 except at the margin, there in rather indistinct radiating series. 

 Me. to Conn. Europe. 



Common as a thin green film on pebbles in pools and at low 

 water mark, along the New England coast ; probably elsewhere. 



Family 3. PRASIOLACEAE. 



Filamentous or membranaceous ; cells with star-shape chro- 

 matophore and one pyrenoid ; asexual reproduction by segment- 

 ation of the frond, by akinetes and by aplanospores; sexual 

 reproduction unknown. Fresh water or marine. 



KEY TO THE GENERA OF PRASIOLACEAE. 



i. Frond normally of a single series of cells, occasionally expanding 

 laterally to two or a few series. i. SCHIZOGONIUM. 



