208 
XVI IIYMEXOPHYLU'M. 
The Tunbridge Film Fern is a slender delicate species, 
having a black thread-like creeping caudex, which is often 
matted and entangled, forming, along with the moss which 
accompanies it, a thick close turf over rocks and stones, and 
is furnished with a few scattered hair-like scales. The 
fronds ore lateral, adherent, small, and of tender membra- 
nous texture, from one to four inches high, somewhat lan- 
ceolate ovate, pinnate, the pin- 
na? distichous vertical alternate, 
once or twice pinnatifid, and 
connected by a wing extending 
along the rachis, the pinna;, 
wings, and involucres all lying 
in the same plane. The pinna:, 
moreover, though sometimes 
branched alternately, have a 
decided tendency to ramify on 
the anterior rather than the 
posterior side. The ultimate seg- 
ments are linear obtuse, with a 
prominent central vein, and a 
spinulosely serrate margin. The 
fronds may be considered as a 
series of stiff branched veins, 
furnished with a membranous 
wing throughout, except in the 
lower part of the stipes, which latter varies from one third 
to one half of, or equal to, the length of the fronds. The 
sori are usually borne by the first vein on the anterior 
side of the pinnae, thus becoming supra axillary. Devia- 
tions from this may be sometimes observed, in which, 
from the involucres and their contents having taken 
the place of the lobes of the leafy part of the frond, 
the identity of origin between them becomes manifest ; 
in fact, in ordinary cases, the fructification takes the 
place on the fertile pinna, of the first superior lobe of 
the barren pinme. The spore-cases are collected into a 
roundish mass upon the receptacle, which is formed of a 
[Hymenophyllum 
tunbridgense.] 
