350 ON THE INSECTIVORA OF THE NEW WORLD. [June 2, 



Strait at a time wlien the continents were united at that point, fori 

 have examined specimens of Sorex vulgaris and of S. minutus from 

 higher latitudes, namely, from the banks of the Khatanga and of the 

 Olenek rivers within the Arctic Circle. 



The Red-toothed Shrews are, in fact, pre-eminently boreal iu 

 their distribution, braving the most rigorous climates of the northern 

 parts of both hemispheres, and thinning out quickly, to finally 

 disappear altogether as we advance south. Their limit appears to 

 be a climatic rather than a territorial one : thus their southern extent 

 in the Palgearctic Region may be very correctly stated to be bounded 

 by the isothermal of 60° Fahr. ; the few exceptions noticeable, such 

 as the presence of species of Soriculus south of this line on the 

 southern slopes of the Himalayas, being easily accounted for by the 

 fact that these animals are rarely found there at a lower elevation 

 than 6000 feet, where they enjoy a really temperate climate. This 

 explains how it happens that Shrews are wholly absent from South 

 America. Two species only are found in Central America, where 

 they extend as far south as Costa Rica, being, like the species of 

 Soriculus \ stragglers from the north along the high mountains and 

 elevated table-lands, and therefore enjoying, like them, a com- 

 paratively temperate climate, their further advance southward being 

 evidently prevented by the long depression which separates the 

 mountains and elevated plateau of Costa Rica from the Andes, and 

 not by the competition of other animals in the Neotropical Region, 

 as writers on geographical distribution would have us believe. The 

 high temperature of the Isthmus of Panama has, in fact, proved as 

 effectual a barrier to these inhabitants of a boreal zone as the low 

 temperature of the ancient northern isthmus between Asia and 

 America was of old to the sun-loving White-toothed Shrews. 

 There cannot be the least doubt that had a snfiicient number of in- 

 dividuals of any of the species of White-toothed Shrews effected an 

 entrance into North America, they would speedily have found their 

 way into the southern part of that continent and thence into South 

 America, and have continued to exist and multiply there. 



Similar remarks apply to the Talpidce, the species of which are, 

 like those of the Red-toothed Shrews, restricted to the temperate 

 and sub-boreal zones of the Northern Hemisphere, the instances in 

 which there appears to be an exception to this rule, as in the case of 

 two species which are found on the southern slopes and spurs of the 

 Himalayas, being accounted for by the high elevation of the districts 

 which they inhabit. Of the seventeen known species, four only are 

 found in the New World, and these have much the same distribution 

 as the Red-toothed Soricidce, the chief difference noticeable being 

 that none have been found as yet north of the southern parts of the 

 shores of Hudson's Bay nor to the south of Mexico, the high tem- 



'^ These have hitherto been supposed to be limited to the southern slopes of 

 the Himalayas ; but I have recently discovered, in the collection of the Paris 

 Museum, a specimen of Soriculus caudatus from the mountains of Western 

 Fo-Kien, China, so that it is probable that this genus has really its head- 

 quarters in countries to the north and north-east of the Himalayas. 



