laevis.
| 14. Penium
|
| 1. | Frond granulate or striate | 2
|
| Frond smooth | 3
|
| 2. | Granules arranged in longitudinal rows | margaritaceum
|
| Granules scattered | Cylindrus
|
| 3. | Endochrome transversely divided into four portions | interruptum
|
| Endochrome not divided into more than two portions | 4
|
| 4. | Frond lanceolate, fusiform or elliptic | 5
|
| Frond cylindrical | 6
|
| 5. | Frond elliptic; fillets undulating | Digitus
|
| Frond lanceolate or fusiform; fillets straight | closterioides
|
| 6. | Ends truncate | truncatum
|
| Ends rounded | 7
|
| 7. | Sporangium orbicular; conjugated fronds deciduous | Jenneri
|
| Sporangium at first quadrate ; conjugated fronds persistent | Brebissonii
|
| 15. Docidium
|
| 1. | Frond neither constricted nor inflated | ?asperum
|
| Frond constricted; segments mostly inflated at the base | 2
|
| 2. | Suture inconspicuous; segments not inflated | minutum
|
| Suture distinct; segments inflated at their base | 3
|
| 3. | Frond stout; suture projecting at the sides | 4
|
| Frond slender; suture not projecting | 5
|
| 4. | Segments with one inflation; extremities attenuated | truncatum
|
| Segments with several inflations; extremities not attenuated. | nodulosum
|
| 5. | Extremities clavate | clavatum
|
Extremities not clavate | 6
|
| 6. | Ends bordered with tubercles | Ehrenbergii
|
| Ends destitute of tubercles | Baculum
|
| 16. Closterium
|
| 1. | Frond suddenly constricted at each end into a conical point | attenuatum
|
| Frond not constricted at the ends | 2
|
| 2. | Frond striated, tapering into a beak at each end, lower margin prominent at the middle | 3
|
| Frond not rostrate; if stnated, its lower margin not prominent at the middle | 6
|
| 3. | Beaks setaceous, as long as or longer than the body | 4
|
| Beaks linear, much shorter than the body | 5
|
| 4. | Beaks much longer than the body | setaceum
|
| Beaks about as long as the body | rostratum
|
| 5. | Frond much inflated at the middle, rapidly tavering at each end | Ralfsii
|
| Frond slightly inflated at the middle, gradually tapering at each end | lineatum
|
| 6. | Frond minute, acicular. sporangium cruciform | 7
|
| Frond not acicular; sporangium orbicular | 8
|
| 7. | Ends obtuse | Cornu
|
| Ends acute | acutum
|
| 8. | Frond semilunate or semilanceolate, the lower margin inclined upwards at the ends | 9
|
| Frond having either truncate ends or its lower margin inclined downwards at the ends | 12
|
| 12. | Vesicles numerous, scattered | Lunula
|
| Vesicles in a longitudinal row | 10
|
| 10. | Ends of frond slightly curved upwards; striae distinct | turgidum
|
| Ends of frond straight; striae none or indistinct | 11
|
| 11. | Frond linear-lanceolate; ends conical, obtuse | acerosum
|
| Frond semilanceolate; ends subacute | lanceolatum
|
| 12. | Frond smooth, crescent-shaped | 13
|
| Frond either not crescent-shaped or else distinctly striated | 17
|
| 13. | Vesicles numerous, scattered | Ehrenbergii
|
| Vesicles in a longitudinal row | 14
|
| 14. | Empty frond colourless; ends rounded | 15
|
| Empty frond usually reddish; ends subacute | 16
|
| 15. | Lower margin of frond inflated at the middle | moniliferum
|
| Frond not inflated at the middle | Jenneri
|
| 16. | Frond inflated at the middle | Leibleinii
|
| Frond slender, not inflated at the middle | Dianae
|
| 17. | Lower margin of frond inclined upwards at the truncate ends; striae none or indistinct | didymotocum
|
| Ends of frond inclined downwards ; striae distinct | 18
|
| 18. | Striae three to seven, prominent | 19
|
| Striae numerous, fine | 20
|
| 19. | Frond semilunate or crescent-shaped | costatum
|
| Frond linear | angustatum
|
| 20. | Frond narrow-linear, nearly straight | juncidum
|
| Frond tapering, curved | 21
|
| 21. | Striae crowded; sutures one to three | striolatum
|
| Striae not crowded; sutures usually more than three | intermedium
|
| 17. Spirotaenia
|
| | Spire solitary, broad, conspicuous | condensata
|
| Spires several, narrow, obscure | obscura
|
| 18. Ankistrodesmus
|
| | | falcatus.
|
| 19 Pediastrum
|
| 1. | Lobes of marginal cells bifid or truncato-emarginate | 2
|
| Lobes of marginal cells entire | 3
|
| 2. | Cells four | Tetras
|
| Cells seven, circularly disposed round a central one | Heptactis
|
| Cells eleven, circularly disposed round five or six central ones | biradiatum
|
| 3. | Marginal cells crescent-shaped; connecting substance coloured | Selenaea
|
| Cells not crescent-shaped; connecting substance hyaline | 4
|
| 4. | Cells granulate | granulatum
|
| Cells smooth | 5.
|
| 5. | Lobes of marginal cells terminated by obtuse processes | ellipticum
|
| Lobes of marginal cells acute | 6
|
| 6. | Marginal cells with notches as wide as the cells | pertusum
|
| Notches much narrower than the cells | 7
|
| 7. | Marginal cells four | simplex
|
| Marginal cells more than four | 8
|
| 8. | Six cells circularly disposed round two central ones | Napoleonis
|
| Cells arranged in two or more circles | 9
|
| 9. | Lobes of marginal cells angular, not tapering | angulosum
|
| Lobes of marginal cells tapering | Boryanum
|
| 20. Scenedesmus
|
| 1. | Cells obtuse | 2
|
| Cells acute or acuminate | 3
|
| 2. | Cells cylindrical or oblong | quadricauda |
| Cells ovate | obtusus
|
| 3. | Cells ventricose at the middle | 4
|
| Cells slender, not at all ventricose | 5
|
| 4. | Cells in a single Zigzag row | acutus
|
| Cells either in two rows or not zigzag | obliquus
|
| 5. | Outer cells crescent-shaped, inner straight, all approximate | dimorphus
|
| Cells curved, distant | duplex
|