THE GREEN ALGAE OP NORTH AMERICA 31 



Page 159, for Key to the Species of Oocystis, substitute, 



i. Outer wall of the family thickened at the poles. 2. 



i. Outer wall not thickened at poles. 4. 



2. Individual cells thickened at poles. 3. 



2. Individual cells not thickened at poles. 7. O.parva. 



3. Many chrotnatophores. 3. O. solitaria, 



3. 1-2 chromatophores. 2. O. lacustris. 



4. Families often united in colonies by successive persistent walls. 10. 



4. Families not united in colonies. 5. 



5. Cells with thickening at poles. 6. 



5. Cells not thickened at poles. 8. 



6 Cells with polar thickening projecting internally. 8. O.nodulosa. 



6. Cells without internal projection. 7. 



7. Cells with concave sides and pointed ends. 9. O. panduriformis. 

 7. Cells with convex sides. 4. O. crassa. 



8. Cells elongate-ellipsoid, about 2.5 diam. long. n. 



8. Cells proportionally broader, ends more broadly rounded. 9. 



9. Cells 9-17 fj. long. i. O. Borgei. 



9. Cells 33-40 M long. 6. O. Naegelii. 



10. Poles rounded. 5. O. novae-semliae. 



. 10. Poles acute. n. O. gloeocystiformis. 



ii. Chromatophores 1-2, with pyrenoid ; cells mostly solitary. 



12. O. rupestris. 



ii. Chromatophores 10-20, without pyrenoid : cells usually in families. 



10. O. elliptica. 



Page 79 of Supplement, after description of O. NOVAE- 

 SEMLIAE, add, Var. MAXIMA W. & G. S. West, 1894, p. 13, 

 PI. II, fig. 25. Cells 2-3 times larger than in the typical form, 

 19-23 X 12-15/1; family of 2-4 cells, 40-52 X 23-42/1. Wis., 

 G. M. Smith. Europe. 



7. O. PARVA W. & G. S. West. 1898, p. 335; 1900, PI. 

 CCCXCIV, figs. 14-17. Cells mostly solitary, but sometimes 

 in families of 2-4 cells; ellipsoid, 6-12 X 4-7 /*, ends slightly 

 pointed, not thickened, wall firm ; chromatophores 2-3. Wis., 

 G. M. Smith. Europe. 



8. O. NODULOSA W. & G. S. West, 1894, p. 15, PI. II, fig. 

 31. Cells oblong-ellipsoid, end rounded with papillate thicken- 

 ing, projecting internally ; cells 25-30 X 16-18 ft, solitary or two 

 in the much broadened mother cell wall. Wis., G. M. Smith. 



Europe. 



9. O. PANDURIFORMIS var. MINOR G. M. Smith, 1916, p. 

 471, PI. XXIV, fig. 2. Cells ovoid with somewhat concave 



