304 SCOTT. [Vol. XI. 



happened that the different characters of structure are so vari- 

 ously and puzzlingly combined among the several groups of the 

 order. 



Protoceras (Marsh). 



The type specimen of the genus is an imperfect skull 

 described by Marsh under the name P. celer (No. 5, p. 81), 

 which is characterized by the presence of a small pair of pro- 

 tuberances, resembling horns, from the parietal bones. Sub- 

 sequently Osborn and Wortman (No. 8) showed that the type 

 specimen belonged to a female and described the male skull, 

 which is one of the most curious fossils ever found and which 

 displays very remarkable secondary sexual characters. They 

 also described and figured the fore and hind feet, which differ 

 in the most striking way from what the structure of the skull 

 would lead us to expect. In the explorations of the Princeton 

 Expedition of 1893 Mr. Hatcher collected a large number of 

 female skulls and one nearly complete skeleton, the material 

 which forms the subject of the present paper. During the 

 season of 1894 Mr. Hatcher has added considerably to this 

 material and has visited the spot where the type of the genus 

 was collected, in order to establish its exact stratigraphical 

 position, which was previously unknown. 



I. The Dentition, 



The dental formula is i^, ^ i>/|j ^^^f> which differs from 

 that believed to characterize Gelocns in an additional upper 

 premolar, although it is not certain that Pj_ may not have been 

 present in the latter genus also, 



A. Upper Jaw (PI. XXI, Figs, i and 2). — The incisors have 

 entirely disappeared, leaving no traces of alveoli in the pre- 

 maxillaries. In the female the canine is rudimentary, but in 

 the male it forms a long curved tusk, comparable to that of the 

 tragulines, though rather shorter and of entirely different 

 shape. While in the latter it forms a compressed scimetar- 

 like blade, in Protoceras it is trihedral like that of the oreo- 

 donts, but relatively longer, more compressed and slender, and 



