DAKOTA AND NEBRASKA. 49 



a median frontal suture appears to have existed in part or throughout the whole 

 extent of the bone, but is obscured by the contiguous fractures. 



A comparatively good view of the palatine region is observable in the second 

 mentioned specimen of 5! crucians, as seen in figure 3. The alveolar borders form 

 prominent ridges diverging to their posterior extremity, where they become continu- 

 ous with the zygomata. Between the ridges the palate is strongly arched. 



The posterior prolongation of the palate forms a cylindroid canal, compressed from 

 below upwards and opening inferiorly by a remarkably narrow interval extending 

 between the pterygoid bones. The under part of the prolongation exhibits a pair of 

 strong ridges converging posteriorly to the pterygoids. External to the ridges the 

 palate bones are impressed in a concave manner. 



The palate bones together anteriorly form a triangle reaching as far forward as the 

 middle of the first true molar. On each side it is pierced by a longitudinal row of 

 posterior palatine foramina, three in number, decreasing in succession. 



A wide and deep crescentoid notch is observed to separate the posterior extremity 

 of the alveolar ridge from the palatine prolongation. 



The orbits have the same form as in H. horridus. The entrance to the lachrj'mo- 

 nasal duct, to the infra-orbital canal, and the spheno- and pterygo-palatine foramina, 

 hold the same relative position as in the Wolf. 

 The optic and spheno-orbital foramina are about half an inch apart. 

 The lower jaw is like that of H. ho7-ridus, hut the bone is more convex in the 

 greater part of its length, and the coronoid process is proportionately rather longer. 

 Three mental foramina occupy the side of the chin. 



The first specimen mentioned of Hycenodon crxicians contains complete series of 

 both upper and lower molars. The canines and incisors are lost in all the specimens, 

 except in one fragment which contains an upper canine tooth. 



The molar teeth present no striking or obvious differences from those of H. 

 horridus, excepting in a few instances. 



The upper sectorial molar is longer in proportion with its breadth, and the back 

 portion is more strongly curved outwardly than in H. horridus. The first upper true 

 molar has a well developed tubercle at the fore jjart of its base, not existent in the 

 latter species. 



The first lower premolar, lost in the fossils of the other species of Hycenodon, is a 

 peculiar looking tooth. The crown is a broad, low cone, with its back border twice 

 the length of the front, and with the fore part of its base reaching a considerable 

 distance in advance of the single fang, which is very obliquely inserted downward 

 and backward. 



Dr. Hayden's last collection of Mauvaises Terres fossils has ailurdud me the oppor- 



7 



