ON GENERA AND SPECIES. 41 
Dicksonies. Gen. 6. (Ex. Dicksonia, Hypoderris, Woodsia.) 
Balantiem. Gen. 4 (Ex. Balantium, Leptopleuria, Cysto- 
dium.) 
Cibotiew. Gen. 1. (Cibotium.) 
2. HELICOGYRATEZ. 
Cyathem. Gen. 7. (Hz. Alsophila, Hemitelia, Amphides- 
mium.) 
Thrysopteridee. Gen. 1. (Thrysopteris.) : 
Besides his general work on Polypodiacesw, M. Fée has 
also published several memoirs on special genera, accom- 
panied by figures, one forming a volume devoted to the 
tribe Acrostichew, 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 eharacter 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 Cyathee the 
80 called obliquity of the ring is more apparent than real. 
Tn my arrangement of 1841 I have stated my views on 
this point. I have there explained that the apparent 
obliquity of the ring in Oyathee 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 
