SYNOPTICAL ARRANGEMENT. 7 



Sub-tribe 2. Connectmy membrane siibpersistent ; frustules after self- 

 division attached by a gelatinous cushion, or dichoto- 

 mous stipes. 



7 Genkra. Synedra, Doryphora, Cocconema, Gomphonema, Po- 

 dosphenia, Rhipidophora, Licmopliora. 



Sub-tribe 3, Connecting membrane evanescent, or obsolete ; f'ustules 

 after self-division united into a compressed filament. 



12 Genera. Meridion, Bacillaria, Himantidium, Odontidium, Den- 

 ticula, Fragilaria, Eucampia, Achnanthes, Diades- 

 mis, Rhabdonema, Striatella, Tetracyclus. 



Sub-tribe 4. Connecting membrane subpersistent ; frustides after self- 

 division united into a zigzag chain. 



6 Genera. Diatoma, Grammatophora, Tabellaria, Ampbitetras, 

 Biddulphia, Isthmia. 



Sub-tribe 5. Connecting membrane subpersistent as a siliceous annidus; 

 frustules after self-division united i^ito a cylindrical 

 filament. 



3 Genera. Podosira, Melosira, Ortliosira. 



Tribe II. Frustides invested with a gelatinous or membranaceous envelope. 

 Sub-tribe G. Frond indefinite, mammillate ; frustules scattered. 



1 Genus. Mastogloia. 



Sub-tribe 7. Frond definite, compressed or globular ; frustules scattered. 



2 Genera. Dickieia, Berkeleyia. 



Sub-tribe 8. Frond definite, filamentous ; frustules in rows. 



3 Genera. Encyonema, CoUetonema, Schizonema. 

 Sub-tribe 9. Frond definite, filamentous ; frustules fasciculated. 



1 Genus. Homoeocladia. 



