274 THE BRITISH FERNS. 
Fronds herbaceous, deep-green, smooth, triangular, tripinnate, 
four to twelve inches high including the stipites, the leafy portion 
being about three or four inches long, and the same in breadth. 
Pinne unequal, ascending, the lower pair considerably largest, two 
inches and a half long, obliquely ovate, the posterior pinnules twice 
as long as the anterior ones; the next pinne are also unequal-sided, 
the posterior pinnules being largest, but this difference becomes less 
manifest upwards. Pinnules (the larger posterior ones) ovate, pin- 
nate; the smaller upper ones pinnatifid. The basal pinnulets of 
the larger pinnules are ovate with a distinct narrowed stalk-like 
attachment, but connected by a narrow wing, pinnatifid, with 
oblong-ovate obtuse lobes, which are cut into linear teeth, the teeth 
generally bifid at the extremity. In its ultimate divisions this 
species is thus very much like C. regia. 
Venation of the pinnules, consisting of a nearly straight costa or 
midvein, with alternate veins directed one into each lobe; a venule is 
given off towards each tooth, and is continued to the margin, where 
it is lost in the sinus formed by the bifid apex of the tooth, thus 
ending in a depression rather than a projection of the margin. 
Fructification occupying the whole under surface. Sori consisting 
of numerous moderate sized, roundish masses of spore-cases, medial 
on the veins, indusiate. Indusium,a delicate transparent, concave, 
subrotund membrane, irregular at the margin, placed at the back of 
the sorus, and soon obliterated. Spore-cases obovate. Spores oblong 
muricate. 
Duration. The rhizome is perennial. The fronds are annual; 
they appear about May, and are renewed at intervals, perishing early 
in autumn. 
This plant is at once known from the other British species of 
Cystopteris by its long creeping caudex, and its triangular and 
tripinnate fragile fronds. It has much more the aspect of Poly- 
podium Dryopteris, for which it might, perhaps, be mistaken, and 
all the more readily, as its indusia become soon obliterated, and the 
sori then seem to consist of round naked masses of spore-cases. It 
is not, however, three-branched, as that is, and is also more divided, 
as would be seen by a comparison of the fronds. 

