eluded in three principal groups or orders, the characters and 

 genera of which are stated below. 



I. POLYPODIACE^E. 



Thecse collected in sori on the back or margin of the frond, pel- 

 lucid, reticulated ; invested by an articulated, elastic, more or less 

 complete annulus or ring. Vernation circmate. 



The annulus is a continuation of the stalk of the theca ; in other 

 words, it is the middle vein of the minute circinate leaf that forms 

 the latter, which is torn open by its extension. 



* Annulus vertical. 



1. Polypodium. 6. Athyrium. 11. Pteris. 



2. Woodsia. 7. Asplenium. 12. Allosorus. 



3. Lastrea. 8. Scolopendrium. 13. Adiantum. 



4. Polystichum. 9. Ceterach. 



5. Cystopteris. 10. Blechnum. 



** Annulus horizontal or oblique. 

 14. Trichomanes. 15. Hymenophyllum. 



II. OSMUNDACE.E. 



Fructification developed upon depauperated portions of a more 

 or less compound frond. Thecse stalked, membranaceous, reti- 

 culated, destitute of annulus, opening vertically with two valves. 

 Vernation circinate. 



16. Osmunda. 



III. OPHIOGLOSSACEJE. 



Fructification developed upon depauperated simple or compound 

 fronds. Thecae sessile, coriaceous, opaque, without any trace of 

 annulus or reticulation, bivalvular. Vernation straight 



I O 



17. Botrychium. 18. Ophioglossum. 



