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Show 1891.] ON THE INSECTIVORA OF THE NEW WORLD. 349 2. Note on the Derivation and Distribution of the Insectivora of the New World. By G. E. DOBSON, M.A., F.R.S. [Eeceived April 24, 189].] Of the ten Families into which the Insectivora are divisible, two only1, and these very closely allied, namely Soricidce and Talpidce, are represented in the N e w World, and of the first-named family, composed of eleven genera, three genera only-Sorex, Blarina, and Notiosorex (with a single species)-have representatives in that continent, where all are restricted to the Nearctic Region. O n the other hand, the closely connected Palaearctic Region includes representatives of no less than eight genera, nearly four-fifths of the whole. All the species of the two genera inhabiting the American continent belong to the Red-toothed Shrews, and are, in fact, modified forms of either Sorex or of Soriculus, the former common to both the Palaearctic and Nearctic Regions, the latter found only in a limited portion of the north-eastern parts of the Eastern Hemisphere, but represented in the Nearctic Region by the species of Blarina. While the species of Blarina are characteristic of the Nearctic Region, those of Sorex are, with few exceptions, closely related one to another, so much so as to be, in m y opinion, Nearctic local races only of two well-known Palaearctic species, namely S. vulgaris and S. minutus ( = S. pygmceus), of whicb the former extends to North America, and the latter is represented there by its but slightly m o dified descendant S. personatus ( = S. cooperi) and its varieties. The Nearctic Shrews were therefore evidently derived from the Palaearctic Region, having migrated from thence probably at a comparatively recent period, if we may judge from the fact that the Water-Shrews of the N e w World are still referable to the genus Sorex, the changes in their bodily structure due to their altered mode of life not having yet advanced nearly so far as we find in the much more highly specialized Water-Shrews (Crossopus) of the Old World. Assuming then, as I believe we are entitled to from a consideration of the above-mentioned facts, that the American Shrews were derived from the Paleearctic Region, it is only reasonable to suppose that the immigration took place by the shortest route, namely, from west to east. The total absence of the White-toothed Shrews from the Nearctic Region goes far to prove that the place of entrance of the ancestors of the American Shrews from the Asiatic continent must have occurred at some position north of N . lat. 50°, for one species at least of the genus Crocidura extends as far north as the region of the Ussuri river2. However, there is no difficulty in supposing that the entrance took place in the latitude of Behring's 1 Not taking into account the Solenodontidce, the species of which are limited to the islands Cuba and Hayti. % A tributary of the A m u r Eiver, in E. Manchuria. PROC. ZOOL. Soc-1891, No. XXIV. 24 |