178 BULLETIN 16 9, UNITED STATES NATIONAL MUSEUM 



The distinction thus is reduced to a matter of size. To judge this 

 I have taken a single dimension, the length of M2, because it seems to 

 be a valid indication of cheek-tooth or gross individual size and can 

 be measured in a relatively large number of individuals. Other 

 dimensions give similar results and all need not be published here. 

 There are in all 24 individuals of the genus Claenodon from the Torre- 

 jon in the American Museum collection in which the length of M^ 

 can be measured. The small species hitherto confused with C. pro- 

 togonioides is obviously distinct, and the following data apply only 

 to the C. ferox-corrugatus group. 



4; 5-1 



CoJculatec/ probable ^Nzotypa^C. corrugatus^ 

 position of type^'] ( 



Type,C.feroX' 



C. corvugatas. 

 f — Type, C. n. sp. Ma tth 



lew. 



£ 



^ 7.8 8.3 8B 9Z 9.8 10.3 10.8 11.3 11.8 12U3 )?.8 13.3 13.8 M.3 



Figure 35.— Histogram of lencth of M2 of Claenodon from the Torrejon of New Mexico in the American 



Museum. 



The statistical data on the length of Mg of the group are as follows: 



Number in sample 18 



Observed range 11. 5 - 13. 9 



Mean 12. 68± 0.25 



Standard deviation 1. 06± 0.18 



Coefficient of variation 8. 3 ± 1.4 



Contrary to some (e.g., Klahn) of the few paleontological workers 

 who have used any statistical data but the most elementary, I can- 

 not agree that the extent of variation ("Variationsbreite"), in this 

 case 2.4 mm (11.5 to 13.9), has any valuable connotation, being so 

 dependent on accidents of sampling that the probable error is enormous. 

 The same fundamental idea is more correctly conveyed by the stand- 

 ard deviation. The above data are calculated from raw measure- 

 ments to 0.1 mm, but in the histogram (fig. 35) these are grouped in 

 units 0.5 mm wide, because of the small size of the sample and because 

 0.1 is certainly too refined a measurement and below the limits of 

 mechanical error and errors due to crushing of the specimens, etc. 



