Marsh — New Reptiles from the Laramie Formation. 449 



ing Mammalia. All three have certain points of resemblance, 

 but differ widely in other respects. Their exact relations to 

 each other and to other mammals are still uncertain, but future 

 discoveries may at any time clear the matter up. 



One fact is becoming more and more evident, the near 

 affinity of the early Primates, Carnivores, Ungulates, and 

 Eoclents, with each other and with the Insectivores, and more 

 remotely with Marsupials. The key to the mystery lies con- 

 cealed in the great break between the lower Wahsatch, at the base 

 of the Eocene as now known, and the Laramie beds of the Cre- 

 taceous. In the latter, none of the above placental mammals 

 have been found, but in the early Eocene occur, side by side, 

 Carnivores, Rodents, and Ungulates, the last represented by 

 both typical Perissodactyles and Artiodactyles, and even some 

 of their subdivisions. The AmMydactyla of large size, the 

 Tillodontia also large, and the diminutive Mesodactyla, all 

 apparently lived together in this period, and a comparison of 

 their special characters points ont their probable lines of descent. 

 The convergence of these lines makes every discovery in the 

 earlier geological horizons of importance, and a connection 

 with the Mesozoic Mammalia may at any moment be demon- 

 strated. The Edentates are evidently a later development, as 

 are also the Sirenians and Cetaceans. 

 New HaveD, Conn.. April 16, 1892. 



Art. LY1L — Notice of New Reptiles from the Laramie 

 Formation; by O. C. Marsh. 



Among the extensive collections of vertebrate fossils secured 

 during the last few years from the Ceratops beds along the 

 eastern base of the Rocky Mountains, remains of reptiles 

 largely predominate, and many have already been described by 

 the writer. A number of new forms of much interest have 

 recently been secured, and some of these are briefly noticed 

 below. The presence of Ophidians and true Lacertilians 

 among the gigantic forms of Dinosauria is especially note- 

 worthy, as their discovery has long been expected. The new 

 Dinosaurs described confirm previous indications, that this 

 subclass, before its extinction, developed into many highly 

 specialized forms, of which suggestions, at least, were seen in 

 those from lower horizons. The large number and variety of 

 these specialized forms could hardly have been anticipated, and 

 they make prominent the probability that the Reptilian age 

 reached its culmination near the close of the Cretaceous. 



