5G0 A R C II yE T II E II I U M O E N E B K A S K A. 



The face is elongated, as in the Hog, but is not compressed laterally, as in 

 Hyracotherium, but is demi-cylindroid, narrowing anteriorly. 



The nasal bones extend as far back as to be on a line with the anterior margin 

 of the orbit. They very gradually increase in breadth for two inches from behind, 

 and then again gradually decrease. They form a continuous convexity with the 

 maxillary bones. The frontal projects between the latter and the former, on a line 

 with the posterior surface of the last premolar. The malar and lachrymal bones 

 advance upon the face to about half an inch of the same line. 



The hard palate is strongly arched from side to side. 



ADMEASIJREMKNTS. 



Estimated length of liue of posterior five molars, .... 4^ 



Distance between tlie second true molars, . . . . . ] f 



Height of face on a line with the last premolar, .... 3 



Height on a line with the second true molar, .... 4 



Breadth of face above the second true molar, . . . . 8 3^ 



The species was dedicated to the late Dr. Samuel George Morton, formerly 

 President of the Academy of Natural Sciences of Philadelphia, and author of 

 Crania Americana, Crania Egyptiaca, etc. 



Since writing the preceding description of the specimens upon which Avere esta- 

 blished the Archaiothcrium Mortoni, I have had an opportunity of examining an- 

 other and very important Iragment of the same animal, which until now had not 

 arrived from Dr. Owen's residence in Indiana. It belongs to the same collection 

 of Nebraska fossils which form the basis of this part of Dr. Owen's Report. The 

 specimen consists of the greater portion of the cranium proper, the right side of 

 which is nearly entire, part of the forehead and face without the nasal bones and 

 anterior extremity, and portions of both sides of the lower jaw (Tab. x., 1-3). It 

 belonged to a young animal, as the sutures generally are separable, and the tempo- 

 rary teeth had not yet been shed. 



In the upper jaAv (Tab. x., fig. 1) of the specimen upon the right side are pre- 

 served in place the second and third temporary molars, and the three permanent 

 true molars, the last of which still remained concealed within the jaw. On the 

 other side the posterior permanent premolars have been exposed, and the anterior 

 two permanent molars are in place. In the fragment of the right side of the lower 

 jaw (Tab. x., fig. 2) a portion of the last temporary molar and the first permanent 

 molar are preserved, and a part of the last permanent premolar is observed within 

 the jaw at its anterior broken extremity. The other fragment (Tab. x., fig. 3) 

 very much crushed, contains the three permanent true molars, the last of which 

 had not yet protruded, a portion of the last temporary molar, and the last perma- 

 nent premolar, which is partially exposed at the broken end of the specimen. 



The skull (Tab. x., fig. 2) is quite peculiar in its form from that of any existing 

 animal, and among known extinct species was probably most like that of CliaTo- 

 potamus, to which Archa)otherium is very closely allied. The cranium proper, in 

 the great extent and general form of the temporal fossce, separated by a high sagittal 



