_Bibliography of Cetacea._—D. F. Eschricht, _Untersuchungen über die Nordischen Wallthiere_, 1849, contains a copious bibliography of the group up to the date of publication. Since that time numerous monographs on special families and genera have been published, and a large illustrated general work, _Ostéographie des Cétacés_, by P. J. Van Beneden and P. Gervais, 1869-80. Besides those already referred to in the footnotes, the following may be mentioned; viz. J. F. Brandt, “Untersuchungen über die Fossilen und Subfossilen Cetaceen Europa’s,” in _Mém. de l’Acad. Imp. de St. Pétersbourg_, 7ⁱᵉᵐᵉ sér. vol. xx. 1873; C. M. Scammon, _Marine Mammals of the N. W. Coast of North America_, 1874; W. H. Flower, “On the characters and Divisions of the Families of the _Delphinidæ_,” _Proc. Zool. Soc._ 1883, p. 466, and _List of the Specimens of Cetacea in the British Museum_, 1885; F. W. True, “Review of the Family Delphinidæ,” _Bull. U.S. Nat. Museum_, No. 36, 1889; P. J. Van Beneden, _Histoire Naturelle des Cétacés des Mers d’Europe_, 1889. For fossil forms, in addition to the works of Van Beneden, Gervais, and Brandt, already cited, the reader may refer to various memoirs published by the former writer in the _Bull. Ac. R. Belgique_ and _Ann. Mus. R. Hist. Nat. Belg._ See also R. Lydekker, “The Cetacea of the Suffolk Crag,” _Quart. Journ. Geol. Soc._ vol. xlii. p. 7 (1887), and _Catalogue of the Fossil Mammalia in the British Museum_, pt. v. (1887). CHAPTER IX THE ORDER UNGULATA Under this term may be included provisionally a large and rather heterogeneous group of mammals, the existing members of which form the Pecora and Belluæ of Linnæus, the Ruminantia and Pachydermata of Cuvier. A few years ago it was found convenient to restrict the order to a well-marked and distinctly circumscribed group, comprising the two sections known as Perissodactyla and Artiodactyla, and to leave out such isolated forms as the Elephant and Hyrax; but the discovery of a vast number of extinct species, which could not be brought under the definition of either perissodactyle or artiodactyle Ungulates, and yet are evidently allied to both, and to a certain extent bridge over the interval between these and the isolated groups just mentioned, makes it necessary either to introduce a number of new and ill-defined ordinal divisions, or to widen the scope of the original order so as to embrace them all.