74 SINCLAIR— HYRACODONS FROM THE 



skeleton in the Princeton University Geological Museum (Nos. 11414, 

 11415, Fig. 8) monographed some years ago by Professor Scott^^ as 

 Hyracodon neb rase en sis. 



Here also a series of individual variants may be arranged, using 

 the length of the molar series as our basis for comparison : 



Princeton Geol. Mus. No. 12705 molar series, length 59 



Princeon Geol. Mus. No. 12702 molar series, length 64 



Princeton Geol. Mus. No. 11414 molar series, length 64 



U. S. National Mus. No. 138 molar series, length 65 ^^ 



Princeton Geol. Mus. No. 10803 molar series, length 72.5 



The horizon of Leidy's specimen is unknown. Of the others. 

 No. 12705 is from the lower zone of rusty nodules of the Oreodon 

 beds, No. 12702 from the upper nodular zone of the same. No. 11414 

 from the Upper Oreodon beds, and No. 10803, the type from the 

 Protoceras-Leptauchenia beds of the Upper Oligocene. Once more 

 I am convinced that these are only individual variations, and that, 

 while there is a gap of a little over ten per cent, between the last two 

 members of the series, additional specimens, when available, will 

 close it. 



Fig. 4. Hyracodon leidyanus, No. 10802 Princeton University Geological 

 Museum. Upper premolar-molar series of the left side, crown view, three 

 fourths the natural size. The tip of m ^ appears just above the gum and is 

 not shown in the drawing. 



To the fourth species, described under D, Mr. Troxell's name, 

 Hyracodon leidyanus, seems entirely applicable. In Fig. 4 is shown 

 the upper premolar-molar series of an incomplete skull and lower 

 jaws. No. 10802 of the Princeton collection, from the rusty nodular 

 layer above the Protoceras sandstones in Corral Draw, in which the 



1* W. B. Scott, " Die Osteologie von Hyracodon Leidy," Festschrift fiir 

 Carl Gcgcnbaur, Leipzig, 1896. Pp. 353-384- Three plates. 



IS In Fig. 13, PI. XIV., " Ancient Fauna," this dimension is 62 mm., show- 

 ing that the figure is not quite natural size. 



