DET 74 
MR. W. MITTEN ON THE MOSSES OF THE EAST INDIES. 3 
genera have been founded by M. Schimper, cannot be trusted to 
afford a sufficient character : for in Climaciwm and Cylindrothecium 
the species occasionally produce thec® which are in no way dif- 
ferent from the unequal-sided form so general in Hypnacee ; and 
it appears to be a general law, that the more the theca is inclined 
or pendulous, the greater is the development of the peristome. 
The form of the calyptra, whether dimidiate or mitriform, is also, 
as furnishing a generic character, to be taken with some caution : 
thus, it serves only to perplex the student to separate Gumbelia 
from Grimmia, and Conomitrium from Fissidens, by such a cha- 
racter, unless it be accompanied by some differences in the other 
organs of the species. Meteorium is here separated from Tra- 
chypus, the first being understood as a modification of Hypnum, 
the second bearing the same relation to Leskea; but Hedwigia, 
Hedwigidium, and Braunia, though distinguished by scarcely any 
other character than the calyptra (which passes through forms 
analogous to those observable in Grimmia), are here united and 
joined with Leucodontacee, to which they have the closest affinity 
in the structure of their leaves and mode of growth; for in these 
days sections cannot be arbitrarily distinguished as acrocarpous 
or pleurocarpous, when in Fissidens the fructification is produced 
from any part of the stem, and when bryologists have not been 
able readily to discover to which section Braunia should be 
referred. 
The groups, as here understood, are founded upon a difference 
in the mode of growth, or in the structure of the leaves: this last 
character has received but little attention from bryologists gene- 
rally ; but by it alone Bryacee are readily separated from Mniace«, 
and JVeckeracee from Hypnacee, and these from Leskeacee. The 
presence or absence of the nerve has been taken advantage of to 
separate Bridel’s Stereodon from Hypnum, the character serving 
rather as a ready means of ascertaining the place of a species than 
as offering any considerable struetural difference; yet it will be 
observed that the species most nearly allied to each other by this 
division fall together. A separate order of Hookeriacee has not 
here been maintained, the sole affinity between its component 
groups being derived from the calyptra. Rhacopilum has been 
removed from Zypopterygiacee, with which it has no affinity, and 
placed in Leskeacee. The section here called Mematodonti pre- 
sents a peristome whose structure appears to be sufficiently dif- 
ferent from that of other mosses,—in Polytrichiacee the so-called 
teeth being composed of adglutinated inarticulate filaments. 
B2 
