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OR the purposes of this article the term Rocky Mountains will be understood to mean the states and territory including and surrounding these mountains in the United States; that is to say, New Mexico, Colorado, Wyoming and Montana. The area thus indicated, stretching from north to south, and including both mountains and plains, is of course extraordinarily varied. Because of the different conditions of temperature, moisture, soil, etc., found within its borders, it possesses as a whole a fauna and flora extremely rich in species. It offers, in the high mountains and to the north, a large assemblage of circumpolar types, some exactly like those of northern Europe and Asia, others variously modified. It gives us, on the plains and to the south, a series of species of Austral origin, some of them intruders even from the tropics. Still again, in its valleys and forests, it has developed a large number of endemic types, found nowhere else in the world.

Such a region necessarily presents great attractions to the naturalist. It has been visited by numerous government expeditions and private individuals, beginning early in the nineteenth century, for the purpose of collecting its scientific treasures. It has yielded to these an abundant harvest, not only of living animals and plants, but also of fossil forms. Every museum of any consequence contains Rocky Mountain material, and innumerable publications are devoted to its description and illustration. These being the facts, a superficial observer might very well conclude that the natural history of the Rocky Mountains was thoroughly known. So far, however, is this from being true that it would be more correct to say that the scientific study of Rocky Mountain biology has hardly begun.

Any one who examines the published accounts of Rocky Mountain animals and plants will find, at least in the majority of groups, little more than descriptions of species. Putting aside the enormous number of species still undescribed, we find that the 'known' species are in fact very little known at all. Among the insects, for instance, there are hundreds of which we do not even know the locality, nearer than the name of the state, and those of which we know the life history are comparatively few. The details of geographical distribution, the