196 
HISTORY OF BRITISH FERNS. 
except on the lower part of the short stipes, by a narrow, 
membranous, leafy margin. The clusters of spore-cases 
are produced around the axis of a vein, which is continued 
beyond the margin of the fronds, this vein or receptacle 
being enclosed within an urn-shaped involucre, consisting 
of two nearly orbicular compressed valves, which are 
spinosely serrate on the upper margin. 
This species is widely distributed throughout the United 
Kingdom, and is found in many other parts of the world. 
It requires the same conditions for its successful cultiva- 
tion as does the Trichomanes, to which genus the reader 
is referred. 
It is the Trichomanes tunhridgensis of Linnaeus. 
Hymenophyllum unilaterale, Willdenow, 
Wilsoris Film Fern, (Plate XV. fig. 3.) 
This plant is by English botanists most commonly 
called Hymenophyllum Wilsoni, but it is identical with 
H, unilaterale^ a name published long antecedently by 
Willdenow. The species is a small moss-like plant, with 
numerous creeping filiform stems, generally growing in 
dense tufts, and producing a crowded mass of semi-droop- 
