THE RIGID BUCKLER FERN. 
73 
to that of Filix-mas , the pinnules having a flexuous 
midvein, with alternate venules again pinnately 
branched. The sori are borne on the lowest anterior 
branch of each venule, that is, on the lowest veinlet 
on the side next the apex of the pinnule, and are 
covered by a kidney-shaped indusium which does not 
fall away. 
The Rigid Buckler Fern is almost entirely confined 
to a few limestone craggy tracts within a small area 
of the contiguous parts of Westmorland, Lancashire, 
and Yorkshire. The Rev. Gr. Pinder writes : — “I 
met with Lastreu rigida in great profusion along the 
whole of the great scar limestone district, at intervals 
between Arnside Knott (where it is comparatively 
scarce) and Ingleborough, being most abundant on 
Hutton Roof Crags and Farleton Knott, where it 
grows in the deep fissures of the natural platform, and 
occasionally high in the clefts of the rocks ; it is 
generally much shattered by the wind, or cropped by 
the sheep, which seem fond of it. With regard to the 
shape of the frond, I may mention that among some 
hundreds of specimens I found but one or two which 
had the fronds oblong-lanceolate, all being more or 
less triangular, and not having the lower pair of 
pinnaD shorter than those in the upper and middle 
parts of the fronds. The fronds of young plants are 
remarkably triangular. The two forms of fronds no 
doubt depend upon the situation, whether sheltered 
or otherwise, and on other causes ; still I imagine the 
triangular to be the true form of the plant.” Its 
elevation above the sea appears to range between 
