TRANSACTIONS OF THE SECTIONS. 109 



culations by their adhesion to one another, and are distinguished from the threads 

 of Trichia by annidar, or unilateral, instead of spiral prominences. Abnormal 

 slaters of Trichia furcata are figured by Wigand, combining the spiral threads of 

 Trichia with the annular structure of Arci/ria in one and the same elater, showino' 

 the close affinity of the two genera. The elaters of all the species of Trichia known 

 previous to the discovery of T.Jlac/eUifer are pointed at each end, and not attached 

 to tbe peridium. In the genus Phi/sarum the branched threads are adnate to the 

 peridia at or near the base, as in Trichia Jiariellifer, but they have no spiral pro- 

 jections. Physarum metallicum, Berkl., e'xhibits other characters, found also in 

 Trichia fiacjellifer , viz. a metallic lustre on its peridium, and ilesh-coloured spores. 

 The latter plant is thus described in the ' Annals of Natural History ' for 1866 : — 

 *^ Trichia Jiaijellifer^ n. sp. ; giobosa sessilis, metallica; flocci apice flagelliferis ; 

 sporis carneis." This species is readily distinguished from its congeners by the me- 

 tallic peridium and colom- of the spores, and from Phimrum by the spiral bands 

 of its threads, which appear to be four or five in number ; its spores are smooth and 

 subgiobose, and measure 0-0003 to 0-0004 inch in diameter; -svhere the elaters branch 

 ofi'a line of junction is perceptible a considerable way below the point of imion, the 

 same spirals involving both threads. We may regard" these gradations of structure 

 in the genera Arci/ria, Trichia, and Phr/sarum as a proof of the arbitrary nature of 

 generic chaiacters, and, while we are compelled to retain such divisions for our 

 o-mi convenience, we must regard them as merely conventional ; and, not to go 

 the length of some naturalists, who deny the existence of species, even in a modi- 

 fied sense, we are forced to acknowledge that the more each plant or animal is 

 studied and investigated, the more nearly do we find it connected with other 

 mdividuals, the transition often becoming so gradual that it is impossible to say 

 where one species ends and another commences. 



The Mammalian Fauna of North-west America. 

 By Robert Beoavn, F.R.G.S. Sfc, Botanist to the British Columbia Expedition. 



Looking at North-west America as that portion of the country to the west of 

 the Kocky Mountains, north of California, an extended study of its mammalia had 

 led the author to divide it into several zoo-geographical regions, which may be 

 briefly classified as follows : — 



1. The region east of the Cascade Mountains. 



2. The region west of the Cascade Mountains. 



Again, the region between the Rocky Mountains and the Cascade Mountains, 

 i. e. east of the Cascade Mountains, is divisible into : — 



(a) A north-eastern district. (/3) A south-eastern district. 



In the same manner the region west of the Cascade Mountains and between 

 the Cascade Mountaius and the Pacific, can be classed into : — 



(a) A north-western district. (/3) A south-western district. 



3. A mountain-region. 



4. A Uttoral region, divided into four districts. 



(a) Arctic. (y) A northern. 



(/3) Sub-arctic. (S) A southern. 



I. Region East of the Cascade Moimtains. 

 This region extends throughout the whole of North-west America, but ends 

 rather before the termination of forests, the Rocky Mountains, according to Mr. 

 W. II. DaU*, not extending straight north to the Ai-ctic Ocean, but bending 

 ott' to the westward, and uniting -with the Cascade range, to form the Alas- 

 kan Mountains of the peninsula of Aliaska. This latter range is the Northern 

 boundary of the true Pacific tauna, the species of animals as well as plants 

 found to the northward of it apparently belonging (when not members of 

 the Arctic fauna) to the fauna and flora of the east of the Rocky Mountains 



* Proc. Boston See. of Nat. Hist. vol. xii. Nov. 4th, 1868 ; and with map in Petermann's 

 ' Geographische Mittheilungen,' 1869, p. 364, tafel xix. 



