DAKOTA AND NEBRASKA. 315 



In the constitution of the teeth oi Parahippus, they are clearly intermediate to those 

 o? Anehippus of tlie same family and Menjchipims of the equine family. 



The length of the series of upper molar teeth is thirty-one lines. The measure- 

 ments of the individual teeth are as follow : 



Length of crown along median ridge of outer lobes, 

 Length of crown along prominent ridge at junction of do., 

 Antero-posterior diameter, .... 



Transverse diameter, ..... 

 Length of crown of first inferior molar at the middle twin 

 conoidal lobe, ..... 



Antero-posterior diameter of do., .... 

 Transverse diameter, ..... 



Remains of Solipeds of uncertain reference. 



Dr. Hayden's collection of fossils from the Niobrara River contains many specimens 

 pertaining to equine animals, but to which of those I have attempted to characterize 

 in the preceding pages I have been unable to determine. They consist of fragments 

 of lower jaws with and without teeth, numerous inferior molars for the most part 

 isolated, a few incisors, and many bones and fragments of others of the limbs. They 

 were picked up here and there in the loose sands of the Niobrara, in association with 

 the more characteristic specimens already described, together with many other of the 

 fossils noticed in this work. 



The more complete series of inferior molars, and most of the others exhibiting any 

 peculiarity, are represented in plate XIX, with views of the triturating surfaces. 

 Those not represented nor described are so nearly like the former as to render it 

 unnecessary to give a particular account of them. 



The more important specimens are as follow : 



1. The greater portion of the right side of the lower jaw of an old animal. It con- 

 tains the third, fifth and sixth molars, with the fangs of the others. The specimen 

 holds a due relationship in size to that referred to Protohippus perdihis, and may 

 perhaps belong to the same animal. The portion of the jaw resembles the corres- 

 ponding portion in the Ass, and the mental foramen holds the same relative position. 



The teeth retained in the specimen have their crowns worn to such an extent as to 

 be inserted alone by lengthened fangs. The triturating surfaces appear of a highly 

 simple character, as represented in figures 13, 14, plate XIX. No trace remains in 

 the jaw of the early existence of a small premolar. 



The measurements of the specimen are as follow : 



