DAKOTA AND NEBRASKA. 1G3 



Six molar teeth form a closed row in the side of the lower jaw of Meri/codus, as iu 

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



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

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

 the}^ 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 inwardty at the fore part of the corresponding teeth of the latter. 



In the last molar the internal lobes are not defined hy 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 intemiediate in appearance to those 

 of the Sheep and Deer. They are comparatively long, 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 uearl}^ 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 ridges or processes as seen in the second premolar of the Deer, and 

 these processes 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 ofi' in a more t)lunt or less pointed manner. 



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

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



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

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

 great relativelj^ as in the Doer. 



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 cro\vns of the first molar and the 

 premolars 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 j^eiTuanent series. 

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



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

 nent teeth behind as in all other ruminants. The second temporary 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 pei-manent first premolar removed from a fragment of another jaw, containing 



