HYMENOPHYLLUM. 197 



ing, brown-green, half-transparent fronds, averaging tliree 

 or four inches in height. The fronds are of a linear- 

 lanceolate form, and pinnate ; the rachis is usually some- 

 what curved, and the pinnje are convex above, all turned 

 one way, so that the fronds become more or less unilateral ; 

 the outline of the pinnge is wedge-shaped, cut in a digitate- 

 pinnatifid 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 



