THE OSTEOLOGY OF SINOPA, A CREODONT MAMMAL OF 

 THE MIDDLE EOCENE. 



By William Diller Matthew, 



Of the American Museum of Natural History. 



INTRODUCTION. 



During the summer of 1902 the writer, assisted bj^ Mr. Walter 

 Grang-er, spent some weeks in the Bridger basin in southwestern 

 W}' oming-, with the object of determining faunal levels in the Bridger 

 formation. This work was undertaken under the auspices of the U. S. 

 Geological Survey and under direction of Prof. H. F. Osborn, palae- 

 ontologist of the Survey. Although collecting was not the principal 

 object of the expedition, a number of fossils were secured, among which 

 the most important was the finely preserved and nearly complete skele- 

 ton of Smopa, found by Mr. Granger. The specimen was extracted 

 from the matrix by Mr. Charles Christman and very skillfully pre- 

 pared for mounting by Mr. Albert Thomson, both of the American 

 Museum of Natural History. I owe the privilege of describing this 

 rare specimen, which is one of the most perfect fossil skeletons ever 

 discovered in an Eocene formation, to the courtesy of Dr. G. P. 

 Merrill, Head Curator of Geology of the National Museum, and of my 

 honored teacher and friend, Professor Osborn. 



The genus Sinojxi was the first carnivore to be described from the 

 Eocene of this continent. It is the most abundant and characteristic 

 creodout in the Bridger formation and is represented by a number of 

 well-detined species in the Lower and Middle Eocene of North America. 

 It has also been found in the Egerkingen beds of Switzerland, probably 

 Middle Eocene, along with the related genus Proviverra. It is not 

 known to occur in any Upper Eocene beds either in Europe or America, 

 but in the Phosphorites of France, of approximately Lower Oligocene 

 age, the closely allied genus Cynohysenodon is quite common. 



» 



Proceedings U. S. National Museum, Vol. XXX— No. 1449. 



208 



