H YMENOPHYLLUM. 115 



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-pinnatifid 

 way, the lobes being linear-obtuse with a spinulose-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 

 primary rachis they are furnished with a narrow membra- 

 nous leafy wing or border, the primary rachis 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 Filmy Fern seems equally diffused with its allied 

 species, and they are often found in company. This, 

 however, seems to be the more common of the two in some 

 parts of Scotland, and in Ireland. It is widely distributed 

 in other parts of the world. 



