1916] Merriam: Mammalian Remains from Ironside, Oregon 133 



type specimen of H. m. callodonte there are two small folds on the 

 antero-external side of the hypoconid, but these folds are smaller than 

 those in this position on the type of H. anthonyi. In other specimens 

 from the Ricardo beds the structure differs more from that of no. 

 22351 than in the case of the type specimen of H. m. callodonte. 



Of the Hipparion species from the northern end of the Great Basin, 

 N eohipparion leptodc of the Thousand Creek Pliocene shows a single 

 very strong fold on the anterior side of the hypoconid, but the enamel 

 is otherwise comparatively simple and the tooth crown in the type 

 specimen, a second lower molar, is extremely narrow. No specimen 

 of of N. leptode is known. Prom the Rattlesnake Pliocene of the 

 John Day region a specimen with a tooth crown of exactly the same 

 height as the type specimen of H. anthonyi shows the enamel very 

 much simpler and the crown relatively very much thicker trans- 

 versely. Po of Hipparion condoni from the Ellensburg formation is 

 unknown. The enamel pattern in //. condoni is fairly complicated, 

 but there is much less crinkling in long teeth than in the relatively short 

 teeth of the type of H. anthonyi. There is a small fold on the anterior 

 side of the hypoconid in a posterior premolar. The size of the crowns 

 in Hipparion condoni suggests a type near the size of the Ironside 

 specimen. Other characters indicate that the two forms are not 

 specifically identical. 



From such evidence as may be obtained from the single tooth 

 available it may be concluded that no. 22351 from Ironside represents 

 a species distinct from any thus far described in the Great Basin 

 region and that the stage of evolution is not far from that of the 

 Ricardo hipparions. This would indicate that the deposits near Iron- 

 side are of early Pliocene or late Miocene age. 



A single fragment, no. 22355 (fig. 2), of an upper cheek-tooth from 

 the deposits near Ironside consists of a cement-filled fossette with the 

 enamel wall. The wall shows very strong plications, eight folds on 

 one side and four on the other. This fragment evidently represents 

 a Hipparion form similar in character to H. anthonyi, and it may be 

 considered to represent that species. The form of fossette and degree 

 of complication of the enamel folds bordering it suggest the character 

 of the Rattlesnake Pliocene species with most complicated enamel. 



Comparative Measurements 



H. m. callodonte 

 No. 21311 

 Ricardo 

 28.4 

 12. 



P5, anteroposterior diameter 



Pg, transverse diameter across hypoconid 



No. 22351 

 Ironside 

 27.8 mm. 

 11.4 



