70 SINCLAIR— HYRACODONS FROM THE 



and a little under twenty per cent, in others.^ In view of similar, but 

 more complete, series of intermediates to be discussed in the para- 

 graphs to follow, I feel that we are here dealing with individual vari- 

 ations and recognize but one species possessing the characters de- 

 scribed under A and shown in Fig. i, which, I suggest, we agree to 

 call Hyracodon arcidens Cope. 



Turning now to the tooth structure described under B and shown 

 in Fig. 2 A-C . to specimens showing which I believe Leidy's name 

 Hyracodon nebrascensis is applicable, it is quite true, as Mr. Troxell 

 points out, that the original description was without figures (many 

 of them were at that date), and that the drawings accompanying 

 Leidy's memoir on " The Ancient Fauna of Nebraska " show, as Mr. 

 Troxell observes, " a widely diversified group." While Dr. Leidy 

 did not always designate his early types in subsequent publications 

 dealing with them, he frequently figured them there carefully, and, in 

 this particular case, his reference to the type specimen is sufficiently 

 detailed to make its identification from the figures practically certain, 

 as will appear from the following considerations : 



Mr. J. W. Gidley has kindly placed at my disposal a so-called 

 " type " of Hyracodon nebrascensis preserved in the United States 

 National Museum (No. 138 of their vertebrate palseontological col- 

 lection). This is the specimen figured on Plate XllA, Fig. 6, of 

 Leidy's " Description of the Remains of Extinct Mammalia and 

 Chelonia " from D. D. Owen's " Report of a Geological Survey of 

 Wisconsin, Iowa and Minnesota; and Incidentally of a Portion of 

 Nebraska Territory," Philadelphia, 1852. Comparison of the speci- 

 men with Fig. 13 of Plate XIV., "Ancient Fauna," will show that it 

 is the same as the one there figured, for the artist has faithfully ren- 

 dered certain minor breaks in the teeth which make identification 

 unquestionable, but the drawing, as reproduced, is a little smaller 

 than the natural size. In the first of the publications just referred 

 to, Leidy states that " this species was first established upon the ante- 

 rior portion of a skull and lower jaw, containing all the molar teeth 

 of an old individual belonging to the collection of the Smithsonian 

 Institution." He then goes on to mention two specimens in Dr. 

 Owen's collections (which are again referred to in the text of the 

 "Ancient Fauna," p. 86), "a head of the same species, of a very old 



