Douglass : Merycochozrus. 85 



In his Extinct Mammalian Fauna of Dakota and Nebraska, pub- 

 lished in 1869, Leidy described and figured part of a skull and a lower 

 jaw, which are designated as the type of Merycochozrus proprius. 

 They are now in the Academy of Natural Sciences in Philadelphia, 

 and I have recently examined them. The skull is represented by 

 portions of both upper jaws, the left the more complete, including 

 portions of the premaxillaries, maxillaries, and malars. The teeth 

 are represented by a third incisor and all the teeth posterior to it. 

 Unfortunately the upper portion of the premaxillary is gone, so that 

 it cannot be ascertained how far the premaxillaries were coossified. 

 It seems a little doubtful, as Mr. Peterson has suggested to me, 

 whether the mandible marked as part of the type belongs to the same 

 individual, as the upper jaw does not quite fit, though this may be due 

 to the defective mending of the mandible. 



In the Extinct Mammalia?i Fauna of Dakota and Nebraska Leidy 

 gives, among others, the following characters, which serve to dis- 

 tinguish this genus from those previously described : Size a third larger 

 than that of Eucrotapims ? {Oreodon) major; the infraorbital arch is 

 remarkable for its great absolute and relative depth, is two and one 

 half times that of Eucrotaphus major, and is directed much more inward 

 to the face than in Oreodon. The anterior origin of this arch is 

 at the anterior portion of the second molar tooth and is not continued 

 forward in a ridge to the middle of the premolar series as in Oreodon. 

 This causes the face to be abruptly narrowed at the interval of the first 

 and second molars. The side of the face "forms a wide unbroken, 

 transverse concavity from the supraorbital arch to the canine alveolus." 

 The infraorbital foramen is large and situated above the interval of the 

 first and second molars. On account of the depth of the malar the 

 orbit is more elevated than in Merycoidodon, and its anterior border is 

 on a line with the interval between the first and second molar. The 

 lachrymal bone appears not to have possessed the depression known as 

 the lachrymal fossa. 



The next species to be included in the genus was Aferycochcerus 

 rusticus. The specimen which is marked as the type is the property 

 of the United States National Museum at Washington. It consists of 

 nearly the same portions as the type of Merycochcerus proprius. It has, 

 however, more of the anterior portion of the muzzle (including the 

 premaxillaries, but none of the nasals) and the symphyseal portion of 

 the mandible. These specimens were collected by Dr. F. V. Hayden 



