FORT UNION OF CRAZY MOUNTAIIsr FIELD, MONT. 



83 



COMPARISON OF SPECIES 



A summary comparison of the lower dentitions of the eight Fort 

 Union species and the other known species of Ptilodus, Paredypodus, 

 and Edypodus is presented in table 9. All figures are means, regard- 

 less of the size or variability of the samples, which are, in most cases, 

 noted elsewhere. Dimensions are in millimeters. The ratios are 

 means of individual ratios, and not ratios of the means of the dimen- 

 sions involved. Fractional serrations and cusps do not exist in the 

 Taw data, but in some cases small or doubtful serrations or cusps have 

 been counted as one-half. 



The known distribution of all American Tertiary species is shown in 

 table 10. 



Table 10. — Known distribution of all American Tertiary species of Ptilodontidae 



• Jepsen now believes (personal communication) that this is older, Paleocene. 



