Marsh — Principal Characters of the Protoceratidce. 171 



The palatine bones are narrow, and bound in front the 

 posterior nares, which extend forward to near the middle of 

 the penultimate molars. The maxillary plates form the roof 

 of the palate forward to the premaxillaries. At their nar- 

 rowest portion, they are deeply grooved for the approaches of 

 the palato-maxillary foramina, which are situated somewhat in 

 advance of the second premolars. The maxillary plates are 

 separated in front along the median line, to receive the posterior 

 branches of the premaxillaries, and on the suture between the 

 two elements, the anterior palatine foramina are in their usual 

 position. The turbinal bones were apparently quite small. 



The Lower Jaw. 



The lower jaw is well represented in Plate II. It is long 

 and slender, especially in front, thus corresponding to the 

 skull. The condyle is broad and strongly convex above. The 

 coronoid process is very short, and its summit is but little 

 higher than the condyle. The angle is rounded and well devel- 

 oped. The ramus expands downward and is thickened beneath 

 the molar teeth, and has a sharp upper edge along the diastema 

 between the first and second premolars. It again extends 

 downward at the symphysis, becoming more robust to support 

 the front teeth. 



The Dentition. 



The dentition of Protoceras is of the early ruminant type, 

 as shown by the short-crowned, selenodont molar series. The 

 dental formula is as follows : 



Incisors — , Canines — , Premolars — , Molars . — . 

 3 ' 1 ' 4 ' 3 



In the male skull, the upper canines are well developed, as 

 shown in Plate II. They are compressed and somewhat tri- 

 hedral in transverse section, and in life formed efficient weapons 

 of warfare. The first upper premolars, a short distance behind, 

 are small compressed teeth, each with two roots ; and after a 

 still longer diastema, the second premolars begin the con- 

 tinuous series. The second and third upper premolars each 

 have a large outer cusp and an inner cingulum, while the 

 fourth has a distinct inner crescent, as shown in Plate V, 

 which also represents faithfully the superior molars. These 

 have all short crowns and the double crescents of true seleno- 

 dont dentition, with a well-developed inner basal ridge on 

 each. The accurate drawings of the accompanying plates 

 render unnecessary a detailed description of these teeth and 

 most of the others here figured. This is true, also, of various 

 minor points in the structure of the skull. 



