DAKOTA AND NEBRASKA. 39 



Hy^nodon horridus. 



The largest species of Hijcenodon of Dakota, distinguished by the above name, 

 probably the most sanguinary and dreaded enemy of its numerous ruminant 

 associates, the Oreodons, etc., greatly exceeded in size any of the described European 

 species; its skull fully equalling that of the largest individuals of the Black Bear, 

 Ursus americanus. 



Of this species we have the opportunity of examining a much mutilated skull, 

 including the jaws and teeth, the greater part of a skull in a less fractured condition, 

 and several small fragments of jaws with teeth from two other individuals. 



Plate III represents the skull of Hyamodon horridus, of which the anterior portion 

 and teeth are taken from thc^rst mentioned specimen, and the posterior portion 

 from the second specimen * 



In general form the skull of Hycenodon horridus is unlike that of any recent 

 animal, and is intermediate in shape to that of the Wolf and that of the Opossum. 

 In comparison with the skull of the Black Bear, nearly the same size, the cranium is 

 shorter and narrower ; the face longer and narrower, but deeper. 



Posterior vieiv of the cranium. — The inion is triangular as in the Wolf, but appears 

 to have projected less at its upper part, and is more hollowed or concave at the sides. 

 The occipital condyle has the same form as in the Wolf, but is more horizontal in 

 position. The occipital foramen appears to have been more circular, or higher in 

 relation with its breadth, than in the latter animal. 



The paramastoid process appears to have been feebly developed in comparison 

 with its condition in the Wolf; the mastoid process is much better developed than in 

 the latter. 



The occipito-mastoid suture descends through the middle of the lateral concavity 

 of the inion. 



A moderately large mastoid foramen pierces the pars mastoidea within a short 

 distance of the lateral border of the inion. 



Superior view of the cranium. — Viewed above, the cranium of Hycenod&ii horridus 

 bears a much more striking resemblance to that of an Opossum than to that of the 

 Wolf, and, indeed, agrees with it also much more nearly in its proportions and 

 relative capacity. It presents an hour-glass shape ; is most constricted a short 

 distance in advance of the middle of the temporal fossse, and expands nearly equally 

 backward and forward. 



A long, high sagittal crest extends from an equally elevated border of the inion to 

 near the middle of the frontal bone, separating the capacious temporal fossae. 



* Back of the dotted line, at the fore part of the temporal fossa, and of that in advance of the last tooth of 

 the lower jaw. 



