Douglass : Rhinoceroses from North Dakota and Montana 265 



Measurements. 



mm. 



Length of skull from tips of nasals to middle of occipital crest 457 



Width of occipital crest 165 



Width of skull at supero-anterior borders of orbits 218 



Length of free nasals 122 



Width of free nasals, posterior 83 



Width of rugosities for horn 35 



Length of rugosities for horn 35 



ACERATHERIUM. 



In August, and again in November, 1905, the writer obtained, at 

 White Butte and in the Little Bad Lands in North Dakota, many 

 remains of rhinoceroses. Among them are two exceptionally complete 

 skulls, one of which has the mandible attached. Though there are 

 some differences in details in the two skulls yet I place them both, 

 provisionally, in the species Aceratherium tridactylum. 



Aceratherium tridactylum Osborn. 



(Carnegie Museum Catalogue of Vertebrate Fossils, No. 1585.) 

 This specimen consists of a skull and mandible which are nearly 

 complete. Small portions of the left angle of the mandible and of 

 the occipital crest had weathered away. It was found in a hard, heavy, 

 green sandstone concretion, or part of a sandstone stratum, just above 

 the nodular Oreodon layer. A stratum of sandstone a little distance 

 away contained many bones and teeth of rhinoceroses and some teeth 

 of horses. Above was a gray, rather soft sandy stratum about fifteen 

 feet in thickness containing the jaws of rodents and remains of 

 crocodiles. 



The specimen differs somewhat from the specimen figured and de- 

 scribed by Osborn in his " Memoir on The Extinct Rhinoceroses." l 

 The nasals are shortened and truncate, not narrowing to a point, or 

 suddenly contracting forward at a point a little distance posterior to 

 the apex, as in Osborn' s figure. There are two incisive alveoli in the 

 premaxillaries, the posterior is nearly as large as the anterior alveolus, 

 and the two are very close to each other. The paroccipital processes 

 are prismatic, having three sides. The mandibular symphysis is quite 

 long and the canine fairly large. The most striking peculiarity of 

 this specimen is its shortened truncate nasals. 



1 Memoirs of the American Museum of Natural History, Vol. I, Part III, April, 

 1898, p. 158, PI. XVII. 



