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Show 75 Fragments of other specimens, probably of this species, present still larger proportions. As compared with the two described species of Stylemys, this species differs in the strong flaring and recurvatnre of its marginal bones, and in the more wedge- shaped caudal marginal bone, as well as its much larger size. Tesiudo Kleitiana, sp. no v. Indicated especially by a caudal marginal bone of a tortoise of larger size than the one regarded as typical of the T. undata. It is, of course, probable that some of the fragments above described without especial reference belong to it. The caudal bone differs from that of T. undata in being nearly plane, and thus wanting the recurvaturo or superior concavity of the corresponding bone of that species. Its form is also quite different. Its lateral sutures are nearly parallel instead of divergent anteriorly, and slightly concave ; if a Ifttle expanded proximally, it contracts again to the suture for the pygal bone. This suture is a short squamosal on the outside of the caudal. The thickness of the bone is almost uniform to near the proximal suture; there an abrupt rabbet commences the plane of the thinner pygal. Measurements. U. Width, proximal 105 Width, distal 110 Length 110 Thickness 019 The free margin is slightly convex. Dedicated to Mr. Francis Klett, of the United States geographical survey, to whose interest in paleontology we are. largely indebted for the opportunity of studying the vertebrate fauna of the Loup Fork beds of New Mexico. GENERAL REMARKS. The line of descent of the horses has been already largely traced by several paleontologists. Another series may now be regarded as partially completed, viz, that of the camels. I have already indicated the antecedent relation in which the Miocene genus Pocbrotherium stands to the existing camels in the structure of the limbs and teeth, as well as the intermediate position occupied by Procamelus in the existence of the iucisor teeth. It now remains to point out the relations determined by the structure of the feet in Procamelus, and the dentition in Pliauchenia, as described in the preceding pages. Commencing with the earliest genus, Pocbrotherium, we have the molar teeth 4- 3, as in the primitive Mammalia generally. There are but two elongate metacarpals, which are not united into a common bone; the lateral ones being rudimental, while thecarpals are of the number characteristic of the Mammalia of all the orders with numerous toes ; namely, seven. In Procamelus of the succeeding formation, the molar formula continues to be 4- 3, but the posterior teeth are more prismatic in form than in the Miocene genus. The incisor teeth are present, thus displaying the primitive character of the class generally; though, as these teeth are early shed, an approximation to the edentulous condition existing in this part of the mouth of ruminants is apparent. In the feet, the approximation to the existing Camelidce is greater than in the dentition. Thus the lateral rudimental metacarpals of Poebrotherium have disappeared, and with them the trapezoides of the carpus. The magnum remains distinct, while the middle metacarpals are united at mil age into a cannon bone. In the contemporary genus Pliauchenia a further modification of dentition is observed As above stated, the molars of Procamelus number - r; in Camelus they number ^ p~ . in Pliauchenia we have the intermediate condition -. "-•. The end of the series is seen in Auchenia, where the formula ' i s 2--~ 3 . a- o It has been observed as a remarkable fact that North America* should present us with the most complete history of the succession of genera which resulted in the horse, and yet should have received this animal by importation from Europe. Nevertheless, the nioie prominent genera of this series have been obtained in the European formations, especially Auchitherium and Hippotherium. But as regards the Camelidce, the genera above described are exclusively North American ; no well- determined form of this group having been found in any formation of the Pakearctic region up to the present time. Until such are discovered, there will be much ground for supposing that the camels of the Old World were derived from American ancestors ; while tbe presence of the llamas in the existing South American fauna'indicates the absence there of tbe conditions which caused their extermination from North America. |
