DAKOTA AND NEBRASKA. 161 



original size. The third premolar is four and three-quarter lines wide, and two lines 

 higli in its present worn condition. 



It niaj be inferred that Protomeryoc, in addition to the number of teeth indicated 

 m the fossil ajjove descriljed, possessed a fourth premolar and three molars. The 

 formula of dentition therefore was the same as in Procamehus, at least for the lower 

 jaw ; that is to say, 3 incisors, 1 canine, 4 premolars and 3 molars. 



In the jaw fragment of Protomeryx the symphysis extends further back in relation 

 with the corresponding teeth than in Procamelus rohnstus or P. occidentalis. The 

 mental foramen also occupies a more posterior position than in the latter, and the 

 second and third premolars are wider in relation with their height, as well as differ- 

 ent in their form. 



I at first attributed the fossil to Leptauclienia, but specimens of the latter subse- 

 quently obtained indicate that it belongs to a different genus. 



The species is named in honor of Prof James Hall, the eminent palgeontologist of 

 Albany, New York, to whom I am indebted for the examination and loan of many 

 interesting fossils, which partly form the subjects of the present work. 



MEGALOMERYX. 



Megalomeryx niobrarensis. 



The above name was employed to distinguish a large extinct ruminant, supposed 

 to belong to the Camel family, and assumed to be of a different genus from Procame- 

 lus or any other one previously noticed, though the grounds of its distinction are of a 

 meagi-e character. It was proposed upon two fossils in Dr. Hayden's Niobrara 

 collection, consisting of inferior molar teeth, one of which is inserted into a small 

 fragment of the jaw. The teeth indicate an animal about as large as the great 

 extinct ruminant, the Merycotherium sibericum, supposed to belong to the Camel 

 family, and likewise founded upon a few molar teeth, which were obtained in 

 Siberia. 



One of the specimens, represented in figure 14, plate XIV, appears to be a first 

 true molar, with the crown between a half and two-thirds worn away, and with a 

 pair of strong fangs inserted into a fragment of the jaw. In form and construction 

 the tooth resembles the corresponding one of the Camel, Lama and Sheep, at the 

 same stage of attrition. The inner side presents a vertical concave groove separating 

 the lobes, and no prominent ridges. The triturating surface presents a yoke-like 

 outline, and a small reniform enamel islet just Ijack of the centre of the hinder 

 division of the crown. The antero-^posterior diameter of tlie crown measures about 



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