Article IX.— TOOTH CHARACTERS AND REVISION 

 OF THE NORTH AMERICAN SPECIES OF THE 

 GENUS EQUUS. 



By J. W. GiDLEY. 



Plates XVHI-XXI and 27 Text Figures. 



CONTExXTS. 



PAGE. 



Principles of Tooth Structure 43 



Tooth Characters as Altered by Age. 94 



Individual Variability tqi 



Revision and Discussion of the Species 108 



Bibliography 139 



In the successive seasons of 1899 and 1900 the writer was sent 

 by Professor Osborn to study more carefully the Paloduro 

 (Goodnight) and Mt. Blanco beds of Texas, both of which Pro- 

 fessor Cope had placed as typical American Pliocene. This study 

 resulted in proving that the Paloduro beds are typical Loup- 

 Fork or Miocene. The Blanco beds are rightly regarded as 

 Pliocene but do not, as Cope supposed, contain any true remains 

 of Equus. In the overlying true Lower Pleistocene or Sheridan 

 Beds the writer found several skeletons which have already been 

 described as Equus sco/ti, sp. nov. In connection with this work 

 it appeared that the Pleistocene American Horses were greatly 

 confused, and Professor Osborn detailed the writer to a thorough 

 restudy and comparison of all the types, which have been carried 

 on under his advice. The general results of this work are 

 summarized at the close of this paper. 



Fossil remains of the genus Equus (indigenous to North 

 America) were reported as early as 1826 by Mitchell,* who re- 

 ferred to this genus some teeth and vertebrae found near the Never- 

 sink Hills in New Jersey, without assigning them to a species. 

 Since that time about twenty different species have been 

 proposed by various authors, based on material found in different 

 localities of the United States and Mexico. 



Although the remains of this genus have been found widely 



^ Catalogue of Organic Remains, New York, 1826, pp. 7 and 8. 

 [91] 



