OF THE FORTY-NINTH PARALLEL OF LATITUDE. 13 
gathered by Dr. Lyall on the west side of the Rocky Mountains 
and in Vancouver Island, and these contain certain species which 
appear to be peculiar to that region, all the species from the 
country on the east side of the Rocky Mountains having been 
previously gathered by Drummond. Considering the vast extent 
of British America with regard to the specimens in herbaria, it 
becomes at once evident that but very little is yet known of its 
Moss-flora beyond the fact that it is very nearly identical with 
that of the north of Europe, and, so far as known, with but few 
peculiar species. A great gap exists in British herbaria in the 
almost entire absence of collections from all that extensive tract 
of country between Davis’s Straits, Hudson’s Bay, and Nova 
Scotia; and as this includes a great extent of regions subject to 
marine influences, it must be expected to produce a very exten- 
sive series of species. 
In the United States, chiefly owing to the zealous labours of 
Sullivant, the knowledge of the productions of the parts investi- 
gated by him and his coadjutors has been greatly increased ; but 
the country is so extensive, and there remains such an unex- 
plored region in the south, where the northern forms become 
exchanged for those of tropical regions, which may probably be 
better observed there than anywhere else, that it is to be expected 
that great additions have yet to be made before the Bryology of 
the United States is approximately exhausted. Besides the spe- 
cies actually collected during the survey, there have been added 
a few others, either overlooked or not before determined, mostly 
collected by Drummond, 
The arrangement of the species contained in the following 
enumeration is different from that employed in the ‘ Musci 
Indici, in which the pleurocarpous genera were arranged ap- 
proximately in the order in which the substance of the leaves 
became more and more indurated and obscure ; and the whole of 
the Hypnoid mosses were divided into two sections by the 
nerves of the leaves, those with a single nerve being considered 
species of Hypnum, and those with two nerves or more were 
referred to Bridel’s Stereodon. But although this plan serves 
very well to break up the tribe into two sections, there occur 
here and there species which may sometimes answer to one and 
sometimes to the requirements of the other section ; examples of 
this occur in the species grouped in Limnobiwm, Schimper, in 
Isothecium, and in Hylocomium, and are probably overlooked in 
many species ; for in some the leaves of the main stem are faintly 
