HYMENOPHYLLUM. 
197 
ing, brown-green, half-transparent fronds, averaging three 
or four inches in height. The fronds are of a linear- 
lanceolate form, and pinnate ; the rachis is usually some- 
what curved, and the pinnae are convex above, all turned 
one way, so that the fronds become more or less unilateral ; 
the outline of the pinnae is wedge-shaped, cut in a digitate- 
piunatifid way, the lobes being linear-obtuse, with a spinu- 
lose-serrate margin. The rigid veins, branching from the 
principal rachis, which is very slightly winged in the 
upper part, become themselves branched so as to produce 
one venule to each segment ; or, in other words, the veins 
are twice-branched, and throughout their entire length, 
after they leave the central rib, they are furnished with a 
narrow membranous leafy wing or border, this rib itself 
being almost quite without any such border. The clusters 
of spore-cases are collected around the free ends of veins, 
which usually occupy the place of the lowest anterior 
segment, and are included within an urceolate involucre, 
which is divided into two oblong convex inflected valves, 
which are quite entire at the flattened edges where they 
meet. 
This kind of Film Fern is equally diffused with the 
allied species ; indeed, it seems to be the more common of 
