156 TUFTS COLLEGE STUDIES, VOL. II, No. 3 



3. Sporangia not specialized. 4. 



4. Thallus a membrane or mass. 10. SCHIZOCHLAMYS. 



4. Thallus a simple or branching filament. n. ELAKATOTHRIX. 

 5. Mature cell solitary. 6. 



5. Mature cells united in colonies. 12. 



6. Mother cell elongate, acicular or fusiform, dividing by oblique 

 walls into daughter cells. 2. RHAPHIDIUM. 



6. Daughter cells formed in the interior of the mother cell. 7. 



7. Cells angular, often with much developed projections. 8. 



7. Cells rounded. 10. 



8. Cells with distinct polyedral central mass. 7. TETRAEDRON. 



8. Cells of rays from a common center, without distinct central mass. 



9- 



9. Rays unbranched. 9. CERASTERIAS. 



9. Rays di-trichotomously divided. 8. THAMNIASTRVM. 



10. Cells with spines. 5. CHODATELLA. 



10. Cells without spines. n. 



ii. Cells ovoid. 4- OOCYSTIS. 



ii. Cells reniform. 6. NEPHROCYTIUM. 



ii. Cells spherical. 3. PALMELLOCOCCUS. 



12. Cells elongate, side by side in a single or double series. 



13. SCENEDESMUS. 



12. Cells arranged symmetrically about a center. 13. 



13. Cells arranged in one plane. 14. CRUCIGENIA. 



13. Cells radiating in all directions. . 14. 



14. Cells lunate or sickle-shaped. 19. 



14. Cells not lunate or sickle-shaped ; united to the centre by gelati- 

 nous strands or stipes. 15. 

 15. Stipes short, unbranched. 16. 

 15. Stipes branched. 17. 



16. Cells with spinous projections. 18. SORASTRUM. 



16. Cells without spinous projections. 17. COEI,ASTRUM. 



17. Cells in series on gelatinous strands. 21. DICTYOCYSTIS. 



17. Cells at the ends of gelatinous strands. 18. 



18. Cells spherical. 19. DICTYOSPHAERIUM. 



18. Cells reniform, ovoid or cordate.' 20. DIMORPHOCOCCUS. 



19. Cells united by the convex sides. 15. SELENASTRUM. 



19. Cells in no definite order in a common gelatinous envelop. 



16. KIRCHNERIELI.A. 



i. ZOOCHLORELLA Brandt, 1882, p. 140. 



Cells free, minute ; spherical, ellipsoid or flattened, with chro- 

 matophore covering part of the cell wall, apparently without 

 pyrenoid ; asexual reproduction by aplanospores formed by suc- 

 cessive division in a cell, freed by rupture of the wall. 



