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MAMMALS OF CHILE OSGOOD33 dogs, deer, cricetine rodents, and other familiar northern forms poured into South America and spread over the entire continent, perhaps having some part in the extinction of the southern types, although doubtless other factors were involved. Southern forms also invaded the north but in smaller numbers and mostly to limited areas.Ground sloths and glyptodonts reached Ohio, Kentucky, California, Nevada, and similar latitudes and there became extinct.Opossums and armadillos now extend to the southern United States, and in tropical Mexico there are anteaters, sloths, monkeys, and several representatives of the hystricomorph rodents. The only form of southern derivation which has attained a very wide range in the north is the porcupine now covering a great part of the United States, Canada, and Alaska.These general features of the history of South American mammals are well known, especially to paleontologists, and of course they are responsible for the broader aspects of present-day distributions, but they cover such vast periods of time and so many elements are lacking that interpretation of details cannot be entirely free of speculation. When applied to Chile they furnish the basis for an immediate division of its modern fauna into one series of southern origin and one of northern.Those of undoubted southern origin are the following, belonging to two orders and eleven genera:

In this early paper certain fundamental points in the history and synonym of the group were for the first time cleared up and the number of known forms was increased from 6 to 21. Five years later the rapid growth of the Biological Survey's collections enabled me to publish descriptions of a dozen additional species and to undertake a new revision of the group, which was brought down to date in 1896. The publication of this revision, with its accompany ing illustrations, and colored maps showing the distribution of the various species, was deferred in order to obtain additional material still needed to settle a few remaining questions of distribution and relationship. This material was subsequently obtained, bringing the total number of specimens available up to 3,000; and my assistant, Mr. Osgood, to whom I had referred certain unsolved problems, undertook to bring the study of the whole group down to date. The result is here offered for publication. Respectfully,

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