162 ON THE EXTINCT MAMMALIA OF 



twenty-one lines, the transverse diameter eleven and a half lines, and the length 

 externally nine lines. 



The jaw fragment is an inch and a quarter tliick. Like most of its associate 

 fossils it is thoroughly petrified, and exhibits the marks of having been gnawed 

 before it became a fossil. 



The second specimen is an isolated first or second inferior molar, slightly Avorn, 

 and represented in figui-es 12, 13, plate XIV. In form and construction it closely 

 resembles the corresponding teeth of the Camel. Its length is about three inches 

 and a third ; the antero-posterior diameter at the triturating surface two inches, and 

 just above the developing fangs an inch and a half At the same stage of abrasion 

 it would have been of the same form as the preceding specimen, and nearly the same 

 size, though not quite so large in its transverse diameter. 



I have latterly suspected that the teeth referred to the above genus may belong to 

 a large species of Procamelus. 



MEKYCODUS. 



Mertcodus necatus. 



The above-named genus and species were origuially proposed on a small fragment 

 of a lower jaw, containing the last premolar and the first true molar of an extinct 

 ruminating animal. The specimen was found at Bijou Hill, east of the Missouri 

 River, and accompanied a large collection of fossil vertebrate remains, from the 

 Mauvaises Torres of White River, obtained for Prof James Hall, of Albany, by Mr. 

 Meek and Dr. Hay den in the summer of 1853. 



.The Niobrara collection of fossils subsequently obtained by Dr. Hayden contains a 

 number of specimens, mainly consisting of fragments of lower jaws with teeth, refer- 

 able to the same extinct animal. 



The most characteristic specimen consists of a portion of the right side of the lower 

 jaw, containing the true molars, the two premolars in advance, and the sockets of the 

 first premolar. It is represented in figure 9, plate XIV, with the addition of a first 

 premolar from another specimen. 



The several fossil fragments of the lower jaw indicate this bone, in advance of the 

 ascending portion, to have nearly the same form and proportions as in the Deer. 



Externally the bone is moderately convex, is deep below the position of the molars, 

 and in advance of them is slender. The base forms a convex line beneath the teeth 

 just mentioned, and turns down toward the symphysis. A long hiatus, as in the 

 Deer, separated the molar teeth from those at the front of the jaw. The margin of 

 the hiatus descends from the premolars in its direction forward. Two foramina 

 occupy the same relative position of the jaw externally as in the Deer. 



