GENERA OF BRITISH FERNS. 49 
1. Polypodium = Dorsal-fruited Ferns, with the circular 
sori exposed, i. e. without covers. 
2. Allosorus.= Dorsal-fruited Ferns, with the roundish 
sori becoming laterally confluent beneath the re¬ 
flexed, unaltered margins of th§ frond. 
§ GYMNOGEAMMEJE = Ferns whose linear clusters 
of spore-cases hare no special covers. It contains 
the genus Gymnogramma. 
3. Gymnogramma =p Dorsal-fruited Ferns, having the sori 
linear, forked, naked. 
§ ASPIDIEJE —Ferns 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. 
§ ASPLENIEiE = Ferns whose sori hare special in¬ 
dusia, of an oblong or elongated form, and springing 
from the sides of the reins . It contains the genera 
Atbyrium, Asplenium, Ceterach, and Scolopendrium. 
E 
