86 



SINCLAIR— ADDITIONS TO FAUNA OF 



[April 24, 



Length of diastema ?c-dp 15 



Depth of jaw below middle of dp 107 



Thickness of jaw at level of mental foramen 45 



Arch.eohippus Sp. 



A small short-crowned pg- of the right side (No. 12128 Prince- 

 ton University Geological Museum, colecting locality lOOoB) agrees 

 in structure with the upper teeth of Archceohippus in the complete 

 union of the metaloph and ectoloph, the distinct protoconule, and 

 open prefossette, there being no anterior median enamel fold on 

 the wall of the metaloph. This horse has not been reported hith- 

 erto from any horizon above the Middle Miocene Mascall beds of 

 Oregon. 



Measurements. 



Greatest anteroposterior diameter 13 



Greatest transverse diameter 13 



Pronomotherium siouense sp. nov. 



Type No. 12057 Princeton University Geological Museum, col- 

 lecting locality lOOoC, the right ramus of the lower jaw with py-m^ 

 and alveoli of iy-c. Tooth crowns worn. A smaller form than 



Fig. II. Pronomotherium siouense, lower jaw, type specimen, external view, 



