99. FILICES. 407 
10. Cereracu. Lateral veins anastomosing, sori attached 
to their middle on the side next the midrib, except in the 
lowest. Indusium (?) a narrow nearly erect membrane on 
the back of the vem. Whole back of the frond covered 
with chaffy scales. 
Tr. IV. ADIANTEA. Thece covered by a marginal or sub- 
marginal elongated part of the frond, or by a separated por- 
tion of the cuticle resembling an indusium. 
11. Buecunum. Thece in a continuous line parallel to the 
midrib upon a longitudinal anastomosing part of the trans- 
verse veins, and covered by a continuous scarious indusium. 
12. Preris. Thece ina continuous marginal line covered by 
a continuous indusium formed of the reflexed margin. 
13. Ap1ianrum. Sori marginal, oblong or roundish, covered 
by distinct reflexed portions of the margin of the frond. 
Suborder I. HYMENOPHYLLACE. 
Thece opening regularly ; ring oblique, excentric, transverse, 
complete; receptacle termmating a vein at the margin of the 
frond. 
Tr. V. HYMENOPHYLLEA. 
14. TrrcHomanss. Thece onan elongated filiform receptacle 
within a cupshaped involucre of the same texture with the 
frond. 
15. HymenopuHyLium. Thece on a narrow subclavate re- 
ceptacle within a two-valved involucre of the same texture 
with the frond. 
** Thece without an elastic ring. 
Suborder III. OSMMUNDACEX. 
Vernation circinate. Rachis woody. Thece regularly 2-valved, 
stalked, in clusters at the extremity of the frond. 
Tr. VI. OSMUNDEA. 
16. OsmunpDaA. Thece clustered, arranged in a branched 
spike terminating the frond. 
