The fresh-water fishes of North America, which form a part of its temperate fauna, extend over very considerable ground; for there is no reason to subdivide into distinct faunæ the extensive tracts of lands between the arctics and the Middle States of the Union. We notice over these, considerable uniformity in the character of the fresh-water fishes. Nevertheless, a minute investigation of all their species has shewn that Lake Superior proper, and the fresh waters north of it, constitute in many respects a special zoological district, sufficiently different from that of the lower lakes and the northern United States, to form a natural division in the great fauna of the fresh-water fishes of the temperate zone of this continent. We have shewn that there are types, occurring in all the lower lakes, which never occur in Lake Superior and northwards, and that most of the species found in Lake Superior are peculiar to it; the Salmonidæ only taking a wider range, and some of them covering almost the whole extent of that fauna, while others appear circumscribed within very narrow limits. Now, such differences in the range which the isolated species take in the faunæ, is a universal character of the distribution of animals; some species of certain families covering, without distinction, extensive grounds, which are occupied by several species of other families, limited to particular districts of the same zone. But after making due allowance for such variations, and taking a general view of the subject, we arrive, nevertheless, at this conclusion; that all the fresh-water fishes of the district under examination are peculiar to that district, and occur nowhere else in any other part of the world.