Mr. Brown on  Lyellia, Leptostomum, and Buabaumia. 567 
essential character of the genus, equally exists in Dawsonia. But 
this outer or spurious calyptra, formed of densely matted hairs 
originating from the vaginula and the apex of the inner cucullate 
calyptra, is wanting in several species of Polytrichum, in some of 
which, and in Lyellia, the true calyptra is furnished with a few 
hairs only, either scattered over the whole of its surface, or con- 
fined to its apex; while in others, as in Polytrichum undulatum, it 
is nearly, and in P. magellanicum and levigatum, entirel y smooth. 
_ Respecting the teeth of the peristomium of Polytrichum, 1 have 
very little to add, except that in P. magellanicum they appear to 
be eighty in number, which is a higher multiple of sixteen than 
has hitherto been noticed in this genus, and the greatest number 
that has yet been found in a single series in the order. 
On the nature of the transverse membrane or tympanum of 
Polytrichum, I have formerly made some remarks in treating of 
Dawsonia, and have there considered it as the remains of the 
pulpy continuation of the columella, originally occupying the 
cavity of the operculum. But its uniform texture, as well as 
its exactly circular form and equal margin remain to be ac- 
counted for; unless this regularity may be supposed to depend 
on the circular, and apparently corresponding, aperture of the 
inner membrane... ; 
Most authors have described the tympanum of Polytrichum as. 
minutely perforated. These pores I have never been able to de- | 
tect; but I observe in many Cases an appearance which may per- 
haps account for the belief in their existence, namely, a minute 
reticulation on the outer surface of the membrane, apparently 
owing to the corresponding areole of the inner surface of the oper- 
culum, with which it was originally in contact. 
Polytrichum is remarkable for the various forms of its capsule. 
Those species, indeed, in which it is quadrangular have been 
| considered 
