

230 THE BRITISH FERNS. 
so-called indusinm, which is either not constantly produced or is 
sometimes not easily found. This inner membrane lies next the sur- 
face of the frond beneath the spore cases, which latter are covered 
by the evident reflexed indusiform margin. We believe when better 
understood this will be found to indicate a structure quite analogous 
to that of the Lindsœœ, the spore-cases lying in a continuous line, 
between an inner and an outer indusium, the latter of which is 
formed from the attenuated margin; differing from Lindsœœ in little 
beyond the fact of the sori being deflected so as to come in contact 
with the under surface of the frond. If this should prove to be the 
ease, it is evident that this group of Pteris must be separated from 
the other larger group in which no inner indusium is found. It 
would in this ease be most convenient as involving the fewest 
changes in nomenclature to distinguish the Ornithopteris or smaller 
group by some other name, leaving the Bupteris or larger group 
under the present name of Pteris. There is good reason to con- 
clude that the structure which occurs in this case is the same as 
that of the long doubtful genus Pesia of St. Hilaire, and if it 
becomes necessary to carry out the separation already hinted at, 
Pasia has the strongest claim to receive the species requiring to be 
removed. For the present, however, our British plant may be left 
in the position it has occupied since the time of Linneus. 
There are various netted-veined species having pteroid fructifica- 
tion, which have been removed to other genera, by far the larger 
proportion of these being included in Litobrochia. Even when thus 
reduced to the free-veined species having the pteroid fructification, 
Pieris forms an extensive and widely dispersed family. 
The name is the Greek pteris, which was applied to some kind of 
fern; itis derived from pteron, a wing or feather, and was no doubt 
used in allusion to the plumy or feathery character of the plants to 
which it was originally applied. 

BRITISH SPECIES. 
P.aquilina: a perennial, with tall bi-tri-pinnate fronds, from a subterraneous 
creeping caudex. 

