Liues. 



Lines. 



Lines 



Gi 



6 





7J 



7 



7i 



10 





8 



4i 



4 





25 



25 





16 



16 



15 



6 



6 





51 



5 



4J 





7 



7 



DAKOTA AND NEBRASKA. 165 



contains portions of lower jaws and teeth of Merycodus necatus, obtained on Little 

 White River, or the South Fork of the main stream. A jaw fragment agrees in 

 character with the Niobrara River specimens, except tliat it is rather more robust in 

 its proportions, the difference being apparently due to difference in age. Its measure- 

 ments, in comparison with the Niobrara specimens, are as follow : 



Specimens from L. White E. Niobrara R. 



Depth of jaw at first premolar, . 



Depth at middle of first true molar, 



Depth at middle of last true molar, 



Depth one-third of an inch in advance of the molars. 



Space occupied by six molars, . 



Space occupied by true molars, . 



Space occupied by last two premolars, . 



Breadth of second true molar, - 



Breadth of last true molar, above, 



MOSCHID^. 



This family is represented in the Mauvaises Terres miocene formation by the 

 remains of an extinct genus, to which I have given the name of Leptomeryx. Its 

 remains were obtained from beds B and D of Dr. Hayden's section. 



LEPTOMERYX. 



The genus distinguished by the above name is founded upon the fossil remains of 

 a small ruminant, allied to the recent Musks, discovered in association with remains 

 of Oreodon Cidbertsoni, 0. gracilis, Anchitlierium Bairdii, &c., in the miocene tertiary 

 deposits of Dakota. The skull of Leptomeryx has the general conformation of that of 

 the Musks, is unprovided with antlers, and has no ant-orbital lachr^yonal fossse. The 

 jaws are provided with continuous rows of six molars on both sides, as in most recent 

 ruminants. 



Leptomertz Evansi. 



The species and genus above named was first characterized by a specimen, consist- 

 ing of a mutilated skull, accomiaanied with a poi'tion of the lower ja\v, discovered by 

 Dr. John Evans in the Mauvaises Terres of White River, Dakota. Subsequently 

 Dr. Hayden obtained portions of several less well-preserved . skulls, together with a 

 multitude of fragments of jaws with teeth, and some portions of other bones of the 

 skeleton, partly from the same region, and partly from Bear Creek, a tributaiy of the 



