ON GENERA AND SPECIES. 41 



Dicksonieaa. Gen. 6. {Ex. Dicksonia, Hypoderris, Woodsia.) 

 BalantiefB. Gen. 4. (i?,?. Balantium, Leptoplenria, Cysto- 



dium.) 

 Cibotiese. Gen. 1. (Cibotium.) 



2. HELICOGTRATEa. 



Cyathefe. Gen. 7. (Ex. Alsophila, Hemitelia, Amphides- 



miam.) 

 Tlirysopteridese. Gen. 1. (Thrysopteris.) 



Besides his general work on Polypodiacese, M. Fee has 

 also published several memoirs on special genera, accom- 

 panied by figures, one forming a volume devoted to the 

 tribe Acrosticheas, in which he arranges the species under 

 nineteen genera. 



Vittaria and its allies form another memoir ; of Vittaria 

 alone he describes and figures no less than twenty-five 

 species and five doubtful, but the examination of numerous 

 sets of specimens justifies me in reducing the number to 

 less than a dozen. 



I have now given a general view of the systematic 

 arrangements of Presl, my own, and Fee's, by which it will 

 be seen that the first important divisional character is 

 derived from the different directions of the ring that sur- 

 rounds the sporangium. My reason for again reverting to 

 this subject is in order to show that in some Gyaihece the 

 so called obliquity of the ring is more apparent than real. 

 In my arrangement of 1841 I have stated my views on 

 this point. I have there explained that the apparent 

 obliquity of the ring in Gyathece is due to mechanical 

 pressure, the sporangia of each sorus being crowded and 

 sessile seated round a columnar elevated receptacle, and 

 each sporangium being inclined upwards, consequently the 

 pressure against each other imparts to them an oblong 

 flattened form especially in the lower part on their inner 



