ANALYSIS OF THE GENERA. 



1 . Frustules nude 2 



„ enveloped in gelatine or enclosed in membranaceous tubes 46 



2. Frustules not forming a filament 3 



„ forming a filament or chain 28 



3. Frustules free or adherent 4 



„ attached by a cushion or stipes 23 



4. Frustules furnished with canaliculi 5 



„ not so furnished 7 



5. Valves arcuate or inflated. Epithemia, 



„ saddleshaped Campylodiscus. 



„ elliptical, ovate or linear 6 



6. Valves concave, alee marginal Surirella. 



„ plane, alse submarginal Tryblionella. 



7. Valves triangular Triceratitjm. 



„ orbicular 8 



„ not triangular nor orbicular 12 



8. Valves striated Cyclotella. 



„ cellular 9 



9. Valves plane 10 



„ undulated Actinocyclus, 



10. Discs of Valves furnished with processes Eupodiscus. 



„ „ not so furnished 11 



11. Valves with a central pseudo-nodule Arachnoidiscus. 



„ without a central nodule Coscinodiscus. 



12. Valves arcuate Eunotia. 



„ not arcuate 13 



13. Valves cymbiform 14 



„ elliptical, oval or linear 15 



14. Nodule subcentral Cymbella. 



„ marginal Amphora. 



