GENERA OF BRITISH FERNS. 49 
1 . Polypodium = Dorsal-fruited Ferns, with the circular 
sori exposed, L e, without covers. 
2. Allosorus = Dorsal-fruited Ferns, with the roundish 
sori becoming laterally confluent beneath the re- 
flexed, unaltered margins of the frond. 
§ GYMWOGRAMME^ = Ferns whose linear clusters 
of spore-cases hare no special covers. It contains 
the genus Gymnogramma. 
3. Gymnogramma = Dorsal-fruited Ferns, having the sori 
linear, forked, naked. 
§ ASPIDIE^ = Perns whose sori hare special indusia, 
of a circular or roundish form^ and springing here 
and there, from the hack of the reins. It contains 
the genera Lastrea and Polystichum. 
4. Polystichum = Dorsal-fruited Ferns, having circular 
umbilicate indusia, attached by their centre. 
5. Lastrea = Dorsal-fruited Ferns, having reniform indu- 
sia, attached by their indented side. 
§ ASPLE]NIE^=jP^m5 whose sori hare special in- 
dusia, of an oblong or elongated form, and springing 
from the sides of the reins. It contains the genera 
Athyrium, Asplenium, Ceterach, and Scolopendrium. 
