A 
We REDE 
THE BRITISH FERNS. 
Gexus XVI: HYMENOPHYLLUM, Smith. 
Gen. CHar.—Sori involucrate, i.e., seated within extrorse-mar- 
ginal oblong or sub-orbicular involucres ; the veins continued to form 
the receptacles, which are short, cylindrical or globose at the apex, 
free, included within the involucres, and bear sessile lenticular or 
turbinate spore-cases. Involucres two-valved. Veins dichotomously 
branched, simple and costa-like in the ultimate segments, or simple 
parallel from a central costa in undivided fronds; venules free. 
Fronds simple, variously pinnatifid, or often decompoundly 
divided, pellucid-membranacéous. 
Caudex rhizomiform, creeping, usually filiform. 
This genus, viewed as a whole, is so exactly the counterpart of 
Trichomanes, that the species of the two genera are quite undistin- 
guishable, except by the technical characters afforded by their invo- 
lucres. The separation of the two groups is however convenient, 
both of them being extensive; though it is perhaps rather to be 
supported on the ground of convenience than on the structural 
importance of the characters on which it is founded, since there are 
some species in which an intermediate condition of the involucres is 
met with; indeed the $ Didymoglossum of the genus Trichomanes 
really stands in this position. In such cases, the difference becomes 
merely one of degree. i 
Like Trichomanes these are Ferns of semi-transparent texture 
and widely dispersed over the tropical regions of both hemispheres. 
The numerous species scarcely admit of assortment in well character- 
ised groups, those which we adopt, namely, $ Hymenoglossum, distin- 
guished by its simple veins from a central costa, and § Hymeno- 
Phyllum, distinguished by its simple costa-like veins in the ultimate 
segments, being very unequal divisions, the former group separating 
only one species, the H. cruentum of Chili. The larger remaining 
group is fairly represented by our native species. Some botanists 
have proposed other divisions founded on the form of the receptacles, 

