2 ARKIV FÖR BOTANIK. BAND 17. N:0 13. 



Systematic account of the more noteworthy species. 

 Borgea gen. no v. 



Cells solitary, free-floating, spherical in shape. Cell wall 

 thin, invested with a tough hyaline gelatinous envelope that 

 is continued in four (rarely 5 — 8) acutely pointed broadly 

 based long processes. Processes of four-radiate individuals 

 quadrately or pyramidately arranged. Cavity of gelatinous 

 sheath containing the cells quadrangular or pyramidal, with 

 a small empty space at the angles between the cell wall and 

 sheath. Cavities of sheath at base of processes or between 

 them, sometimes lacking or reduced to fine nodules. Chloro- 

 plast single, parietal, cup-shaped; with one pyrenoid. 



Reproduction by division of cell contents to form four 

 zoospores (?) that are liberated by a fragmentation of the 

 cell wall into two parts. 



Borgea planctonica sp. nov. Figs. 1—9. 



Characters as described above. 



Diameter of cells without spines 8 — 10 a, with spines 

 25 — 55 |J.; length of spines 12,5—22 u.. 



The distinctive characters of the alga are the small num- 

 ber of gelatinous conical setae and the peculiar angular spaces 

 between the sheath and the cell wall. When these are 

 coupled with the characteristic appearance of the empty cell 

 walls after reproduction has taken place it seems better to 

 consider it a distinct alga that to regard it as a new species 

 of Echinosphaerella G. M. Smith. 



Four-spined individuals were of almost universal occur- 

 rence but a few were observed having more than four spines. 

 In general the four spines are pyramidate in arrangement, 

 though all transitions from the pyramidate to those which 

 have the spines quadrately arranged in one plane may be 

 found. The angular space between the gelatinous sheath 

 and the cell wall is also quite variable; in some specimens 

 it is rather conspicuous (figs. 3—4), in others it appears si- 

 milar to the polar nodules on the walls of Oocystis cells 

 (figs. 2, 7), while again it is completely lacking (figs. 1,6,9). 



