122 
NEW ARRANGEMENT OF 
stoma, or springs from it, within the margin, and a httle 
below the summit of the theca. In the latter case, the teeth 
are generally more or less connected by a membrane, which 
not unfrequently arises to a level with the stoma, or even 
above it. Sometimes all vestiges of the teeth then disap- 
pear, thus presenting the aspect of a truly membranaceous 
peristome, as is seen in Diphysium, Bua^baumia, and Lep- 
tostomum. ; and in such as have a double peristome of re- 
gular teeth, the inner one is formed by this membrane, split 
into a fixed number of attenuated segments. 
Sometimes, though very rarely, the stoma is furnished 
with a dense horizontal epiphragma, not accompanied with 
teeth (as is the case with the epiphragma of Polytrichurn)^ 
an instance of which occurs in Lyellia ; or, what is still 
more curious, is supplied with a pencil of fine capillary ci- 
liae, as is exemplified in Dawsonia. It is remarkable that 
these ciliae apparently arise from around the summit of the 
columella, as well as from the walls of the theca. This, how- 
ever, wiW not appear so singular, when we consider that the 
summit of the columella may nearly fill up the stoma, — and 
that, in the case of a membranaceous peristome, it is not un- 
common for the peristome, or a part of it, to lose its attach- 
ment to the theca, and adhere to the periphery of the summit 
of the columella. This has occurred to ourselves, particular- 
ly in Leptostomum erectum ; and we have little doubt, that 
what Dr Hooker figures as an elongated columella in seve- 
ral of his new Orthotrica is a similar instance thus ren- 
dering their affinity apparently more striking to Schlothei- 
mia of Schwgegrichen : the opercular membrane it will be 
found is not on the summit of, but in the interior of, the 
upright one. 
There are several other modifications of the peristome, 
Musci Exot. Tab. 24. 127. and 128. 
