Professor 0. C. Marsh— The Skull of Profoceras. 437 



separated from it by a well-marked suture, and passing forward 

 above the vomers, which are here distinct. The pterygoids are 

 attached to the posterior border of the palatines, and above to the 

 alisphenoids. There is no distinct alisphenoid canal. 



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 narrowest 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 Jaio. 



The lower jaw is well represented in Plate XIX. It is long and 

 slender, especially in front, thus corresponding to the skull. The 

 condyle is broad and strongly convex above. The coronoid 

 jDrocess is very short, and its summit is but little higher than the 

 condyle. The angle is rounded and well developed. 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 x, Premolars f , Molars f . 



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

 in Plate XIX. They are compressed and somewhat trihedral in 

 transverse section, and in life formed efScient 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 continuous 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. The superior molars have all short crowns and the double 

 crescents of true selenodont dentition, with a well-developed inner 

 basal ridge. 



The teeth of the lower jaws of Protoceras are indicated in 

 Plate XIX, and the full series is shown. The three incisors are 

 directed well forward, and diminish in size from the first to the 

 third. The still smaller canine is situated close to the last incisor, 

 and is similar in form. A long diastema follows, and gives the 

 upper canine freedom of motion. The first premolar is somewhat 

 similar to the corresponding one above, but is larger and directed 



