2 MR. W. MITTEN ON THE MOSSES OF THE EAST INDIES. 
Syntrichia. The arrangement of the Pleurocarpous Mosses in the 
‘Synopsis’ is rather an agglomeration of species than a systematic 
disposition: thus, Neckera is composed of species whose sole 
point of affinity lies in the peristome, which, in all the tribe here 
called Arthrodonti, presents but one typical form, of which the 
highest development is observable in Bryacee, Bartramiacee, and 
in most of the pleurocarpous groups. This peristome consists of 
an external one of sixteen teeth, each of which is composed of 
three series of cells, articulated to each other: the two outer of 
these series are frequently combined into one, but generally 
having the line of division evident, sometimes separating along 
this line, as in Dieranum, Fissidens, Grimmia, and many of the 
Trichostomacee, of rather firm consistence and generally reddish 
colour; and the inner series consists of hyaline bladdery cells (to 
the expansion or contraction of which the hygroscopic action is 
principally due) reaching across the inner side of the two external 
series and closely adherent to them. The internal peristome con- 
sists of a more or less elongated folded membrane, divided above 
into processes, often perforated along the carina, with three cilia 
between each, which at each joint have a small appendage. In 
all the groups to which this structure appertains, no generic im- 
portance is attached to the absence of any part or of the whole 
peristome : thus, the first modification is the absence of the small 
appendages to the cilia; next the cilia themselves are reduced in 
number, shortened, or absent; then the processes decrease in 
width, the supporting membrane is shortened, and finally the 
internal peristome is entirely absent. The external peristome 
presents all stages of development, from the teeth with the in- 
ternal series of cells highly developed and forming “ trabecule,” 
to those in which the series is difficult to observe, if present at 
all; and, as with the internal, the whole external peristome is at 
times wanting. Many stages of the above transitions are obser- 
vable in Bryacee and Bartramiacee ; and as they occur in species 
which in every other particular possess a very close affinity, it 
becomes evident that the genera of Mosses cannot be founded on 
the greater or less development or even absence of an organ which 
is for the most part reducible to a single typical form, except at 
the sacrifice of every character plainly observable in other portions 
of the species. Further, there occur some mosses which produce 
a peristome or not, according as the theca is more or less developed 
and elongated: this is seen in Desmatodon (as here understood) 
and in Encalypta. The form of the theca, upon which several 
