THE GREEN ALGAE OF NORTH AMERICA 53 



here, but American forms and species reported since then have 

 been added. 



Page 176, for Key to the Species of Pediastrum, substitute, 



i. Marginal cells undivided, cuspidate. 8. 



I. Marginal cells bilobed. 2. 



2. Lobes of marginal cells simple. 3. 



2. Lobes of marginal cells emarginate, bidentate or bifid. 7. 



3. Disk continuous. 4. 



3. Disk perforate. n. 



4. Lobes of marginal cells incurved, forcipate. 3. P. forcipalum. 



4. Lobes of marginal cells straight or nearly so. 5. 



5. Margin finely tuberculate-crenulate. 5. P. vagum. 



5. Margin not tuberculate-crenulate. 6. 



6. Lobes ending in short, broadly triangular teeth. 12. 



6. Lobes ending in linear projections. 13. 



7. Disk continuous. 8. P. tetras. 



7. Disk perforate. 9. P. biradiatum. 



8. Marginal cells with a single tooth or cusp. i. P. simplex. 



8. Marginal cells with more than one tooth or cusp. 9. 



9. Marginal cells tridentate. 2. P. tricornutum. 



9. Marginal cells with two projections. 10. 



10. Projections in one plane, short, distant. 10. P. integrum. 



10. Projections long, not in the same plane. n. P. Kawrayskii. 

 ii. Cell wall with a network of very fine ridges. 12. P. sculptatum. 

 ii. Without network. 7. P. duplex. 



12. Cell wall with a rather coarse network of ridges. 



13. P. araneosum. 



12. Without network. 6. P. angulosuin. 



13. Prolongations capitate. 14. P, glandulifertim. 



13. Prolongations not capitate. 4. P. Boryanum. 



Page 178, after description of P. BORYANUM, add, 



Var. LONGICORNE Reinsch, 1867, p. 96. Marginal cells with 

 rounded lobes, each extended in a usually incurved projection, 

 15-30 /u. long. Greenland, Richter. Europe, 



Page 179, after description- of P. DUPLEX, add, 



Var. ASPERUM A. Braun, 1855, p. 93. Cells 8-64, up to 35 p. 

 wide, prolongations short, rough or toothed. Fla., Borge. 



Europe. 



Var. CORNUTUM Raciborski, 1890, p. 101. Cells slightly at- 

 tached, openings irregular, not rounded ; marginal cells sub- 

 cordate, each lobe ending in a long, straight, cylindrical pro- 

 longation. Fla., Borge. Europe. 



