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Show 1883.] OF THE ORDERS AND FAMILIES OF MAMMALIA. 179 present divisions and terminology are no longer sufficient for the purpose ; and some other method will have to be invented to show the complex relationships existing between different animal forms when viewed as a whole. The present time, preeminently distinguished by the rapidly changing and advancing knowledge of extinct forms, is scarcely one in which this can be done with any satisfactory result. All attempts to form a classification embracing even the already known extinct species must be only of a very provisional and temporary nature. There are, moreover, special difficulties in undertaking this subject, to any one working on this side of the Atlantic. It has often been remarked that the centre of gravity of the civilization, arts, literature, and commerce of the world appears to be shifting westward. This is certainly the case with paleeontological discovery. Our knowledge of the ancient condition of animal life on the earth is being revolutionized by explorations in the so-called " N e w World." With regard to Mammals it is a curious fact, that although research has been prosecuted in suitable localities in many parts of Europe and Asia with considerable assiduity since the beginning of the century, scarcely a single form has been found which does not come within the limits of our actual ordinal groups, or which would necessitate any important modification in a classification based upon existing species. But in the N e w World, beginning with the earliest known South-American extinct forms-the Toxodons, Nesodons, Mesotheriums, & c , and passing to the still more wonderful discoveries of the last ten years in the Western Territories of the United States, we find ourselves in completely new realms of life. W e are all at once confronted with numerous highly specialized forms, representing apparently new ordinal groups, and still more numerous generalized forms filling up the intervals, and breaking down the distinctions between nearly all the best-established orders of higher placental Mammals. With these I do not propose to deal in the present communication. The very abundance of the material that has lately come to hand is in itself an obstacle to drawing any satisfactory generalizations from it, as it has not left leisure to the few who have an opportunity of working at it to give such full and detailed descriptions as are necessary for the guidance of those who have not the advantage of examining the actual specimens. In systematic descriptions in books, in lists, and catalogues, and in arranging collections, the objects dealt with must be placed in a single linear series. But by no means whatever can such a series be made to coincide with natural affinities. Tbe artificial character of such an arrangement, the constant violation of all true relationships, are the more painfully evident the greater the knowledge of the real structure and affinities. But the necessity is obvious ; and* all that can be done is to make such an arrangement as little as possible discordant with facts. In preparing the article " M a m malia" for the ninth edition of the 'Encyclopaedia Britannica,' such a scheme had to be framed ; and the chief merit which I claim for it is, that it departs as little as possible from the prevailing, or what mav be called traditional, sequences of arrangement. In the article, |