THE BRITISH FERNS. 
Genus XIII: CYSTOPTERIS, Bernhardi. 
Gun. Onan.—Sori indusiate, rotundate, the receptacles medial. 
Indusium roundish-ovate, fornicate or concave, affixed by its broad 
base, the apex often lacerate, sometimes acuminate. Veins simple 
forked or pinnate from a central costa ; venules free. 
Fronds membranaceo-herbaceous, bi-tri-pinnate. 
Caudex tufted, decumbent, or elongated and creeping. 
This small genus of delicate-fronded Ferns belongs to that group 
in which the sori are dot-like or punctiform, growing from a medial 
point at the back of the veins. The sori are covered by a peculiar 
kind of indusium, which instead of being plane is hollow or concave, 
and is fixed to the vein behind the sorus, so as to cover it like a 
hood. ë 
The affinity of this genus has been variously understood. Thus 
it has been referred to the eyatheaceous series by some botanists of 
repute, to the neighbourhood of Athyrium by others, but more com- 
monly to the Aspidieœ, with which its punctiform indusiate sori at 
first sight seem to have close affinity. We have been led to regard 
it as indicating a peculiar structure, intermediate between the 
Aspidieœ and the Davalliee, and have consequently made it the type 
of a small group called Oystopteridee. 
This group, Oystopteridew, is, as already intimated, one of those 
in which the sori are punctiform, medial, and indusiate. Its dis- 
tinguishing feature consists in the attachment of the indusium, 
which being roundish in general outline, is attached behind the 
spore-cases transversely by its base, the front and side parts being 
free. The Aspidiew on the one hand, differ from this in having 
the indusium attached by its centre or its sinus, and the Davalliee, 
in a restricted sense, differ on the other hand in having the indu- 
sium attached by its base and sides, the anterior portion only being 
free. This is nearly the view taken of the affinities of the genus 

