30 Annals of the Carnegie Museum. 



well-established that the types with true horns and truly titanotheroid 

 cranial structure are of earlier origin than has been hitherto believed. 

 At the same time it appears that the structure of the limbs and feet 

 of these predecessors is more nearly identical with that of the con- 

 temporary genera Telmatherium, Afetarhiniis, DoJichorhinus, etc., and 

 undoubtedly further removed from Titanotherium than are Diplacodon 

 elatum, Protitanotherium emarginatnm, etc., from a later horizon of 

 the Uinta sediments. We learn from the material collected in the 

 Uinta Eocene by the Princeton Expedition of 1886* that the remains 

 referred to Diplacodon are much further advanced in the direction of 

 the Oligocene titanotheres. Comparisons made will be referred to in 

 their proper places in the following description. 



I desire to thank Dr. W. J. Holland for his kindness in allowing 

 me to work up the material on which this paper is based, and for his 

 revision of the manuscript for publication. I am also under obliga- 

 tion to Professor Charles Schuchert and the staff of the Peabody 

 Museum of Natural History for much assistance in connection with 

 the study of Professor Marsh's type of Diplacodon elatum. Mr. 

 Sydney Prentice of the Staff of the Carnegie Museum made the 

 drawings reproduced in this paper, and the photographs were made 

 by Mr. Arthur S. Coggeshall. 



Diploceras osborni^ gen. et sp. nov. 



Type: — Front of skull, lower jaws, portion of pelvis, atlas, portion 

 of axis, fragments of scapula and foot-bones. No. 2859. 



Paratypes: — Front of skull No. 2858; vertebral column, fragments of 

 ribs, limb- and foot-bones. No. 2860; crowns of two upper molars. 

 No. 2860a; humerus. No. 2861; tibiae No. 2862. 



Horizon: — Upper B, Uinta Eocene. 



Locality: — On Duchesne River, near Myton, Uinta County, Utah. 



Generic Characters: — Dentition: If Cy Pf Mf ; Premolar series 

 proportionally long; P- with two distinct internal tubercles; horn-cores 

 well developed; limbs relatively long and slender; tibial trochlea not ex- 

 tended back on the calcaneum. Astragalus high, with long neck, cal- 

 caneal and cuboidnl facets laterally located. 



Specific Characters: — Alveolar borders of the premaxillaries extending 

 well in front of the canines; nasals long and relatively thin, their anterior 



^ Scott, W. B.. and Osborn, H. F., "The Mammalia of the Uinta Formation," 

 Trans. Amer. Philos. Soc, Vol. XVI, 1889, pp. 512-518, pis. IX-X. 

 ' In honor of my early teacher, Professor Henry Fairfield Osborn. 



