IN the autumn of 1870, I discovered, in the Cretaceous of Western Kansas, the remains of a very large swimming-bird, which in many respects is the most interesting member of the class hitherto found, living or extinct. During the following year, other specimens were obtained in the same region, and one of them—a nearly perfect skeleton—I named Hesperornis regalis.1 In subsequent careful researches, extending over several years, I secured various other specimens in fine preservation, from the same horizon and the same general region, and thus was enabled to make a systematic investigation of the structure and affinities of the remarkable group of birds of which Hesperornis is the type. The results of this and other researches were brought together in 1880, in an illustrated monograph.2