DAKOTA AND NEBRASKA. 



47 



Hysenodon horridus. 



Height of lower jaw at condyle, 



. 





15 lines. 





a 



" at coronoid process. 



. 





36 



a 





u 



" at last molar. 



. 19 



lines. 



20 



ec 





a 



" at third premolar. 



. 18 



u 







18 1 



Length of 



symphysis, 



. 42 



(I 







35 



(( 



alveolar border of lower jaw, 



. 80 



a 









a 



upper molar series. 



. 62 



a 







52 



a 



lower molar series, . 



. 68 



a 









« 



upper true molar series. 



. 33 



li 



34 



(( 



27 



a 



lower true molar series. 



. 30 



a 



30 



a 





Breadth of last upper sectorial molar, . 



. 15 



a 



14 i 



a 



m 



Ht^nodon cruentus. 



A second species of Eycenodon from the Mauvaises Terres of White River, 

 Dakota, was founded upon a portion of a lower jaw discovered by Dr. John Evans. 

 The specimen is represented in figure 10, plate V, and contains the third and fourth 

 premolars and the sectorial molar. The species distinguished by the above name, as 

 indicated by the fossil, was between a fourth and third less than H. horridus, and 

 was rather larger than the H. hracliyrhynchus of France. 



The jaw fragment and the contained teeth agree in their form and proportions 

 with the corresponding portions of Hycenodon liorridus. 



The measurements of the specimen are as follows : 



Length of the lower molar series, . . . . . .53 lines. 



Space occupied by the three true molars, . . . . . 25 " 



Antero-posterior diameter of third premolar, . . . . 7 " 



Height of do., . . . . . . . . 6 " 



Antero-posterior diameter of fourth premolar, . . . . 8 " 



Height of do., " . . . . . . . , 7 " 



Breadth of sectorial molar, . . . . . . . 11 " 



Height of do. in front, . . . . . . . 6J " 



Height of do. posteriorly, . . . . . . . 6 " 



The recent collection of Dr. Hayden from the Mauvaises Terres contains a 

 specimen of an upper tooth of a HyGenodon, which bears the proper relative propor- 

 tion to those of the lower jaw above described to belong to the same animal. The 

 tooth is the upper last molar of the right side, and is but little worn. It is repre- 

 sented in figure 11, plate V. From what has been observed in the concluding part 

 of the chapter on HycB7iodon liorridm, both this tooth and the jaw originally referred 



