_Proboscidea._--The Elephantidæ are only represented in America by one species of _Mastodon_ and one of _Elephas_, in the Newer Pliocene deposits. In the Older Pliocene, Miocene, {139}and Upper Eocene, no remains of this order have been found; and in 1869, Dr. Leidy remarked on the small average size of the extinct North American mammalia, which were almost all smaller than their living analogues. Since then, however, wonderful discoveries have been made in deposits of Middle Eocene age in Wyoming and Colorado, of a group of huge animals not only rivalling the elephants in size, but of so remarkable and peculiar a structure as to require the formation of a new order of mammals--Dinocerata--for their reception. This order consists of animals with generalised Ungulate and Proboscidean affinities. The lower jaw resembles that of the hippopotamus; they had five toes on the anterior feet and four on the posterior; three pairs of horns, the first pair on the top of the head, large and perhaps palmated, the second pair above the eyes, while the third and smallest stood out sideways on the snout. They had enormous upper canines, of which the roots entered the middle horn cores, no upper incisors, and small molars. Professor Marsh believes that they had no trunk. The remains discovered indicate four genera, _Dinoceras_ (3 sp.), _Tinoceras_ (2 sp.), _Uintatherium_ (1 sp.), and _Eobasileus_ (2 sp.). Many other names have been given to fragments of these animals, and even those here given may not be all distinct. Another new order, Tillodontia, recently established by Professor Marsh, is perhaps yet more remarkable in a zoological point of view, since it combines the characters of Carnivora, Ungulata, and Rodents. These animals have been formed into two families, Tillotheridæ and Stylinodontidæ; and three genera, _Tillotherium_, _Anchippodus_, and _Stylinodontia_. All are from the Eocene of Wyoming and New Jersey. Perhaps to these must be added _Elotherium_ from the Miocene of Dakota, the other forms being all Eocene. They were mostly animals of small size, between that of the capybara and tapir. The skull resembled in form that of a bear; the molar teeth were of Ungulate type, and the incisors like those of a Rodent; but the skeleton was more that of the Ursidæ, the feet being plantigrade. Professor Cope has since described three new genera from the Eocene of New Mexico, _Ectoganus_, _Calamodon_, and _Esthonyx_, comprising {140}seven species allied to _Tillotherium_ and _Anchippodus_, and having also relations, as Professor Cope believes, with the South American Toxodontidæ.