THE GREEN ALGAE OF NORTH AMERICA 



95 



15-18. Cells solitary, 10-13 M diam., in a spiral of two to many 

 turns, both ends rounded. Minn. Europe. 



Larger than the type, and always in a spiral, usually of many 

 turns. 



5. O. ARBUSCULA (A. Br.) Rabenhorst, 1868, p. 68; Lem- 

 merman, 1899, p. 28 ; Sciadium arbuscitla A. Braun, 1855, p. 49 

 PI. IV; Wolle, 1877, p. 174, PI. CLVII, figs. 1-6 ; Wittr. and 

 Nordst., Alg. Exsicc., Nos. 401, 1360. Cells always united in 

 families, umbellate or corymbose, straight, 3-5 p. diam. ; stipe 

 slender, 2-3.5 /* lon g- connecting the lower end with the basal 

 disk. 



Mass. "Specimens from three or four states." Wolle. Europe. 



6. O. GRACILIPES (A. Br. ) Rabenhorst, 1868, p. 68 ; Lem- 

 merman, 1899, p. 28; Sciadium gracilipes Wolle, 1887, p. 175, 

 PI. CLYII, figs. 7 and 8; Bohlin, 18973, PL I, figs. 27-32, 35, 

 39, 40; PI. II, figs. 59 and 60. Cells in a simple umbel, 5-7^ 

 diam., stipe 10-14 M !ong, to the disk-like base. Minn. Europe* 



3. CHLOROBOTRYS Bohlin, 1901, p. 34. 



Cells globose, with several disk-shaped chrornatophores with- 

 out pyrenoid, with more or less oil ; cells 2-16 united by a hya- 

 line tegument ; asexual reproduction by short cylindrical 

 akinetes, with thickened membrane, formed from vegetative 

 cells ; also by cell division. 



Only one species. 



C. REGULARIS (West) Bohlin, 1901, p. 34, fig. 9; West, 

 !9Q4, p. 254, fig. 119. Cells globose, 10-27 /j. diam., united by 

 a gelatinous coating into families up to 90 fj. diam. including 

 the coating, cells sometimes in contact ; chrornatophores 6-30 in 

 a cell ; asexual reproduction by division of a cell into 2-4 

 daughter cells, also by akinetes. Fig. 3. Common in various 

 parts of Europe, and reported by West from the United States. 



4. CONFERVA Linnaeus, 1737, p. 326. 

 Filaments at first attached by a special basal cell, later free ; 



cells uniuucleate, rarely with two nuclei ; chromatophores disk- 

 shaped, two to many in a cell, without pyrenoid, producing oil 

 but not starch ; cell wall thin, breaking up into H sections. 



*O. CUSPIDATUM (Bailey) Rabeuhorst, 1868, p. 68; Wolle, 1887, p. 176, 

 PI. CL/VIII, figs. 1-2; Closterinni cnsf>idatnw Bailey, in Ralfs, 1848, p. 

 219, PI. XXXV, fig. n ; Xei-HSf/iic/la .' cus^idata De Toni, 1889, p. 614. 

 A problematical plant ; it is doubtful if it belongs to any one of the gen- 

 era in which it has been placed, and it certainly deserves investigation. 

 The cells are crescent-shaped with rounded ends, like a broad Clos- 

 terimn, each end terminated by a stout spine. The cells measure 

 150X165 n, the spines are 15 M long. 



