200 



ON THE EXTINCT MAMMALIA OF 



Antero-posteriov diameter of second upper true molar, 

 Transverse " " " 



Antero-posterior diameter of first upper true molar, 

 Transverse " " " 



Anntero-posterior diameter of last upper premolar, , 

 Transverse " " " 



Antero-posterior diameter of first lower true molar, 

 Transverse " " " 



Antero-posterior diameter of last lower premolar, . 

 Transverse " " " 



Antero-posterior diameter of third lower premolar, . 

 Transverse " " " 



Height of crown of third lower premolar, 

 Antero-posterior diameter of second lower premolar, 

 Transverse " " " 



Height of crown of second lower premolar, . 

 Depth of jaw below last true molar, 

 Depth of jaw below second premolar, 



Lines. 



. 2i 



. 3J 



. 21 



. 3J 



. 2i 



. 3! 



; 2i 



. 2J 



. Si 



. 24 



. 31 



. 2 



. 2i 



. 3 



. 14 



. 2i 



. 5 



. 31 



DICOTYLES. 



Dr. Hayden's collection of Niobrara fossils contains a specimen of an upper canine 

 tooth of a Peccary, represented in figure 3, plate XXVHI. It is much worn, and is 

 nearly the size that the corresponding tooth of Platygonus compressus would appear 

 to be under the same circumstances. It presents a longitudinal median groove both 

 externally and internally. Its reference to any particular species is uncertain. 



NANOHYUS. 



Nanohtus porcinus. 



In the expedition of Dr. P. V. Hayden, in the summer of 1866, to the Mauvaises 

 Terres of White River, Dakota, among the fossil vertebrate remains previously 

 noticed or described, he discovered a fragment of the left ramus of the lower jaw of a 

 small mammal, supposed to be nearly allied if not belonging to the suilline family. 



The teeth in the fragment consist of the last temporary molar, the succeeding two 

 permanent molars in functional position, and the anterior portion of the third molar 

 partially protruded. The interior of the jaw beneath the temporary molar is occu- 

 pied by the crown of the last premolar, which, judging from the appearance of the 

 exposed outer part, has the same form and size as the molars behind. 



