U. S. GEOLOGICAL SURVEY 



MONOGRAPH 65 PLATE LVIII 



UPPER DENTITION IN FOUR SPECIES OF PALAEOSYOPS 



Illuilrating successive ^ages in the evolution of the premolars. (See p. 314.) Dra\vings by E. S. Chri^man. Natural sise. A, Palaeosyops 

 paludosus (Am. Mus. 13032), 5 miles south of Granger, Wyo., level Bridger B 1, pl-m'. B, P. major (Am. Mus. 12182), middle of Ck>tton- 

 vi^ood Creek, Bridger Basin, Wyo., level Bridger B 3, p^-m^, drawing reversed. C, P. rohu^us, type (Yale Mus. 11122), part of upper 

 Bridger formation, probably level C or D, p^-m^, drawing reversed. D, Palaeosyops sp. (Am. Mus, 2361), south of Hayitack Mountain, 

 Washakie Basin, Wyo., level Washakie A, pl-m? 



