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158 the British Isles, but still lives in the Seine, and is still more abundant in the Loire. Another fresh-water univalve (Paludina marginata Michaud), not British, but common in the

south of France, likewise occurs, and a peculiar variety of Cyclas amnica, which by some naturalists has been regarded as a distinct species. With these, moreover, is found a peculiar variety of Valvata piscinalis.

If we consult Dr. Von Schrenck's account of the living mammalia of Amoorland, lying between lat. 45° and 55° North, we learn that, in that part of North-Eastern Asia recently annexed to the Russian empire, no less than thirty-four out of fifty-eight living quadrupeds are identical with European species, while some of those which do not extend their range to Europe are arctic, others tropical forms. The Bengal tiger ranges northwards occasionally to lat. 52° North, where he chiefly subsists on the flesh of the rein-deer, and the same tiger abounds in lat. 48°, to which the small tail-less hare or pika, a polar resident, sometimes wanders southwards. We may readily conceive that the countries now drained by the Thames, the Somme, and the Seine, were, in the post-Pliocene