GENERA. 
The first order of the Ferns is conveniently divided into the sub-orders Nudce 
and IndusiatcB, according as the sori are naked or covered with an indusium. 
The arrangement of the species into Genera depends upon the shape and position 
of the sori, together with the nature, the adherence, and the manner of opening 
of the indusium, when there is one. In the other orders the same principles are 
adopted, as far as their structure will admit. 
As the orders of the Fern Allies contain each but one British genus, the 
characters of that genus are but a recapitulation of those of the order itself. 
NUB/E. 
Sori linear or oblong, scattered Grammitis. 
Sori round, scattered Polypodium. 
IND TJSIA TJE. 
Indusium distinct from the Frond. 
Sorus round. 
Sorus round. 
Sorus round. 
Indusium cleft into capillary segments . Woodsia. 
Indusium cucullate or bladder-shaped . Cistofteris. 
Indusium peltate, either round or reniform Aspidium. 
Sorus linear or oblong, transverse, solitary. Indusium 
from lateral veins, opening towards the midrib 
Sorus linear, transverse, in twin masses. Indusia folding 
over each other, and opening outwardly 
Sorus linear, longitudinal, close to the midrib. Indusia 
opening outwardly 
j- Asplenium. 
j- ScOLOPENDRIUM. 
j- Blechnum. 
Cover part of the Frond itself reflexed. 
Sorus linear, continued around the margin of the frond Pteris 
Sorus on transverse veins, near to the margin 
Sorus in distinct spots, attached to the cover itself 
Thecae in pitcher-shaped, one-valved receptacles 
Thecae in compressed, two-valved receptacles 
Cryptogramma. 
Adiantum. 
Trichomanes. 
Hymenophyllum. 
Thecae petioled, reticulated, terminating in a leafy frond 
Thecae sessile, smooth, in a separate compound spike 
Thecae sessile, smooth, in a separate simple spike . 
OSMUNDA. 
Botrychium. 
Ophioglossum. 
Thecae attached to the root, free, and indehiscent . 
Thecae imbedded in the base of the leaves 
Thecae of two kinds, axillary in a leafy spike, or stem . 
Thecae of one kind, in catkins, terminating a leafless stem 
Pilugaria. 
Isoetes. 
Lycopodium 
Eguisetum. 
