164 F. B. Loomis — New Horse from the Zower Miocene. 



upper and lower jaw. The specimen was found in the upper 

 part of the Lower Harrison beds, 8 miles northeast of Agate, 

 Sioux Co., Nebraska; and is named to honor Prof. J. M. Tyler, 

 the organizer of the Amherst expeditions. 



While having a rather short facial portion, the skull is 

 moderately high and narrow. The individual being described 

 is an adult, only recently matured, as indicated by the moderate 

 wear on the teeth and the fact that the third upper molar is 

 scarcely worn at all. On the upper incisors the pit is deep, 

 being entirely surrounded on the inner side by the raised cingu- 

 lum. This pit seems to be more developed than in P. nebras- 

 Tcensis. A canine is indicated by a small alveolus a short 

 distance from the third incisor. The first premolar is wanting 

 in this specimen. The second to the fourth premolars, while 

 slightly larger, grade into the molars having the same charac- 

 teristics. While the parastyle and the mesostyle are well devel- 

 oped they are not as prominent as in P. nebraskensis. A 

 remnant only of the cingulum is present on the inner part of 

 the front border of each tooth. The protocone and protoconule 

 unite to make a strong protoloph, but are separated from each 

 other by a narrow constriction. On the metaloph of premolar 

 four and the succeeding molars a small crochet is developed, 

 which while distinct does not however unite with any part of 

 the protoloph ; consequently the prefossette is not enarely 

 isolated. The hypostyle is strong and notched in the rear. 



On the lower jaw the pit in the incisors is not as well devel- 

 oped as in incisors of the upper jaw, appearing more like 

 a groove behind a well-marked cingulum. The lower canine 

 is a simple cone of moderate size. The first premolar is indi- 

 cated by a small alveolus and must have been v tray. The 

 remaining premolars and molars each have a well-marked 

 cingulum, starting from the parastylid, continuing around the 

 outer border, and back to a tiny hypostylid. The inner wall 

 of each tooth is relatively straight, the upper part being, in 

 little worn teeth, notched to separate off the strong parastylid, 

 and again between the paraconid and hypoconid. The heel of 

 the third molar is moderate in size and simple in form. 



While very like, and probably ancestral to P. nebraskensis^ 

 this species is distinguished by the less pronounced parastyle 

 and mesostyle, by the relatively narrower teeth, the deeper 

 pit in the incisors, and the smaller size. It is a primitive 

 member of the genus, the crochet not uniting with the proto- 

 loph and cement being entirely absent. 



