antlers. A large four-tusked mastodon is known by numerous fragments and occasional complete bones or large pieces of tusk.
Next to the horses the most numerous of the hoofed animals are the camels. They are known by at least three types. One is a small form of the genus Procamelus. A second and very large type probably belongs to the genus Pliauchenia. A third form with very large long limbs, a larger animal than the living camel, is possibly to be referred to the genus Alticamelus. Other genera may be present in the collection.
Of the remaining fauna, the rodents are represented by rabbits. The carnivores are known by at least eight species, including three large cats, at least one of which is a sabre-tooth with the greatly developed upper canine teeth. Two others may belong to the true cats, represented by the modern puma and wild cat, without the saber-like upper teeth. The dogs include one small form similar to the fox. A second type, Tephrocyon, one of the most characteristic animals of this horizon, is a form considered by many to be possibly the ancestor of the modern dogs and wolves. The most abundant creatures of the dog group are found in one or two representatives of the genus Aelurodon, very large, very heavy-jawed animals, much larger than any modern wolves, and even greatly exceeding the extinct dire wolf, now so well known by abundant skeletons from the asphalt deposits of Rancho La Brea. These animals were evidently not rare. They probably lived off the herds of large ungulates, sometimes bringing down a live animal, sometimes robbing the smaller wolves and the big cats of their prey. Their unusually massive jaws and teeth seem built to serve as bone crushers, and there can be little doubt that* the general state of dismemberment and destruction of all skeletons, and the absence of satisfactory paleontologic materials in the Barstow formation, is due in large part to the destruction of these scavengers.
Birds are, known in the Upper Miocene beds by a few fragments representing an owl. Reptiles are represented by numerous fragments, and several nearly perfect skeletons of a large tortoise resembling in many respects the living desert tortoises of the Mohave.
The fauna of the Upper Miocene is as a whole that of an open country affording fairly abundant grass and herbage, and evidently better watered than the Mohave Desert of the present day. The numerous remains of grazing horses of the Merychippus type, the presence of mastodons, oreodons, of many deer-antelope, a considerable variety of camels, and a wild pig all indicate that grass and other nutritious vegetation must have been more abundant than at present. The relatively small representation of oreodons, and of browsing horses like Hypohippus, and the presence of large tortoises are possibly to be correlated with open semi-arid character of the country.
That small bodies of water were present at times in this area is
