FORT UXIOX OF CRAZY MOUNTAIN FIELD, MONT. 9o 



rPTILODUS DOUGLASSI Simpson 



Figure 9, a 



?Ptilodus douglassi Simpson, 1935d, p. 225. 



Type. — U.S.N. M. no. 9795, right lower jaw with P4-M2. Collected 

 by A. C. Silberhng. 



Horizon and locality. — Gidley Quarry (and two referred specimens 

 from Silberling Quarry), Fort Union, jSIiddle Paleocene horizon, 

 Crazy Mountain Field, Mont. 



Diagnosis. — Mean length P4 (three specimens) 6.6, deviation from 

 mean of P. montanus —1.4, 3.3 times standard deviation of the latter. 

 Length Mi (type) not significantly deviating from that of P. montanus. 

 Katio length P4: length Mi (type) 1.8, deviation from mean P. mon- 

 tanus — 0.5, 12.5 times standard deviation of the latter. Length 

 Ml '.length M2 (type) 1.8, deviation from mean P. montajius-i-OA 

 (standard deviation not calculable, but difference almost certainly 

 significant). Serration and cusp number not significantly different 

 from P. montanus. 



Remarks. — Expressed in other and less definite words, the species 

 is structurally closely similar to P. montanus but differs significantly 

 in its smaller size, relatively much smaller P4, and relatively smaller 

 M2 (or, much larger Mi relative to P4 and Mo). P4 also appears to be 

 somewhat lower in lateral contour, but this cannot be adequately 

 checked . 



No species other than P. montanus resembles this closely enough 

 to demand further comparison. 



7PTILODUS GIDLEYI Simpson 



Figure 9, h 



IPtilodus gidleyi Simpsox, 1935d, p. 225. 



Type.— U.S.N.A'I. no. 9763, left lower jaw with P4 and broken Mi. 

 Collected by A. C. Silberling. 



Horizon and locality. — Gidley Quarry, Fort Union, Middle Paleocene 

 horizon, Crazy Mountain Field, Mont. 



Diagnosis. — Length P4, type, 6.1 (two other specimens 5.9 and 6.1). 

 Length Mi, type, about 2.5. Ratio length Piilength Mj about 2.4, 



