While there is little difference of opinion as to the propriety of including in the family †Hypertragulidæ the four phyla described in the foregoing pages, the systematic position and the relationships of that family as a whole are matters of debate and likely long to remain so. Dr. Matthew refers the entire group to the suborder Tragulina and regards _†Leptomeryx_ as being closely related to the direct ancestry of the American deer, a view which is accepted by Professor Osborn, but in which I am unable to concur. My own belief is that the family was an early offshoot from the cameline stock and therefore referable to the Tylopoda, in which suborder they are here included. It would be out of place to enter upon a discussion of this perplexing problem, which can hardly receive a definitive solution until the artiodactyls of the Uinta stage are thoroughly understood. As in so many other series, the key of the mystery lies hidden in the Uinta fauna, which is still so inadequately known. SUBORDER PECORA. TRUE RUMINANTS This is the most advanced, specialized and diversified group of the artiodactyls, though the ruminating habit is shared by both Tylopoda and Tragulina. In this multitude of forms, giraffes, deer, antelopes, sheep, goats, oxen, buffaloes, bisons, etc., it is difficult to find a clue to a natural arrangement or classification. As a whole, the suborder is a well-defined group, and many structural characters, not all of which is it needful to enumerate here, are common to all of its members. The upper incisors are invariably absent, and, save in a few of the deer, the upper canine also, while the lower canine has become incisiform; the premolars are always three in number in each jaw and the molar-pattern is selenodont throughout. The odontoid process of the axis is spout-shaped. Except in a few deer, the Pecora all have bony outgrowths of the skull in the form of antlers or horns, at least in the males, many females being hornless. The ulna is coössified with the radius and the fibula is lost, except the lower end, which is a separate malleolar bone. There is always, in both fore and hind feet, a cannon-bone, the lower ends of which are parallel, not divergent, as they are in the Tylopoda, and each articular surface is encircled all around by a prominent median keel, as in the horses, which in the other suborders, as in mammals generally, is confined to the posterior side and not visible from the front. (_Cf._ Figs. 220 and 214, p. 401.) In no existing member of the Pecora are there complete lateral digits, and in several modern genera they have been completely suppressed; but in most there is, behind the functional pair of digits, a pair of “dew-claws,” the bones of which are more or less completely reduced, often to mere nodules. The stomach, which in the Tylopoda and Tragulina is three-chambered, is in the Pecora divided into four distinct parts.