DAKOTA AND NEBRASKA. 163 



Six molar teetli form a closed row in the side of the lower jaw o? Merycodus, as iu 

 ordinary recent ruminants, and as represented in figures 9, 10, plate XIV. 



The unworn molars were furnished with long crowns, inserted into the jaw as in 

 the Sheep, and they protruded in the same manner as in this animal gradually as 

 they were worn away. The form and construction of the true molars is almost 

 identical with those of the Sheep, excepting that they are not provided with the well- 

 marked fold extending inwardly at the fore part of the corresponding teeth of the latter. 



In the last molar the internal lobes are not defined hj ridges as in the Sheep, and 

 the posterior division of the crown is fuller, less acute, or is even obtusely rounded at 

 its back part, and the two constituent lobes include a more capacious and deeper 

 interval or pit. 



The crowns of the hinder pair of premolars are intermediate in appearance to those 

 of the Sheep and Deer. They are comparatively loilg, thin, and straight externally 

 as in the former, but their constitution more nearly resembles that of the second pre- 

 molar of the latter. 



The third premolar externally is nearly square, and presents a vertical groove at 

 the back part, as in the corresponding tooth of the Sheep. Internally it presents a 

 succession of five I'idges or processes as seen in the second premolar of the Deer, and 

 these jDrocesses have nearly the same form and relationship with one another as in 

 the latter. The triturating surface, relatively narrower at its back part than in the 

 Deer, is also worn off in a more blunt or less pointed manner. 



The second premolar is a diminished likeness of that just described, but a wider 

 and feebler depression occupies the position of the external groove of the former. 



The first premolar was inserted by a pair of distinct fangs, and appears to have 

 been separated from the teeth occupying the front of the jaw by a hiatus almost as 

 great relatively as in the Deer. 



In the specimen described, the crown of the last molar, worn upon all its lobes, had 

 not yet protruded one-half its length from the jaw. The second molar had protruded 

 about half the present length of its crown. The crowns of the first molar and the 

 premolai's had entirely protruded. 



A second fossil specimen belonging to Merycodus necatus consists of the left side of 

 the lower jaw of a young animal, containing in the functional series of molar teeth the 

 three temporary molars and the first and second true molars of the permanent series. 

 The last permanent true molar had not yet commenced to protrude front the jaw. 



The back temporary molar presents the usual form in its relation with the perma- 

 nent teeth behind as in all other ruminants. The second temjjorary premolar 

 resembles in its constitution the second and third of the permanent series. The first 

 temporary premolar is a diminished representative in form of the one behind it. 



A permanent first premolar removed from a fragment of another jaw, containing 



