COMMON CHARACTERS. Bill hooked, the upper mandible furnished at the base with a soft skin, or “cere,” in which the nostrils are situated. Toes, three before and one behind. _Raptores._ =Strigidæ.= Eyes directed forwards, and surrounded by radiating feathers, which are bounded, except anteriorly, by a circle or rim of differently formed, stiffer feathers. Outer toe reversible. Claws much hooked and very sharp. Legs and toes usually feathered, or, at least, coated with bristles. _The Owls._ =Falconidæ.= Eyes lateral, and not surrounded by radiating feathers. Outer toe not reversible (except in _Pandion_). Claws usually hooked and sharp, but variable. Head more or less completely feathered. _The Hawks._ =Cathartidæ.= Eyes lateral; whole head naked. Outer toe not reversible; claws slightly curved, blunt. _The Vultures._ The preceding characters, though purely artificial, may nevertheless serve to distinguish the three families of _Raptores_ belonging to the North American _Ornis_; a more scientific diagnosis, embracing a sufficient number of osteological, and accompanying anatomical characters, will be found further on. The birds of prey—named _Accipitres_ by some authors, and _Raptores_ or _Rapaces_ by others, and very appropriately designated as the _Ætomorphæ_ by Professor Huxley—form one of the most strongly characterized and sharply limited of the higher divisions of the Class of Birds. It is only recently, however, that their place in a systematic classification and the proper number and relation of their subdivisions have been properly understood. Professor Huxley’s views will probably form the basis for a permanent classification, as they certainly point the way to one eminently natural. In his important paper entitled “On the Classification of Birds, and on the Taxonomic Value of the Modifications of certain Cranial Bones observable in that Class,”[2] this gentleman has dealt concisely upon the affinities of the order _Raptores_, and the distinguishing features of its subdivisions. In the following diagnoses the osteological characters are mainly borrowed from Professor Huxley’s work referred to. Nitzsch’s “Pterylography”[3] supplies such characters as are afforded by the plumage, most of which confirm the arrangement based upon the osteological structure; while important suggestions have been derived from McGillivray’s “History of British Birds.”[4] The Monographs of the _Strigidæ_ and _Falconidæ_, by Dr. J. J. Kaup,[5] contain much valuable information, and were they not disfigured by a very eccentric system of arrangement they would approach nearer to a natural classification of the subfamilies, genera, and subgenera, than any arrangement of the lesser groups which I have yet seen.