66 



BULLETIN 169, UNITED STATES NATIONAL MUSEUM 



2-35 2.75 315 355 3-95 4-35 



LENGTH Ml, HyOPSODONTIDAE 



10 



5- 



P depressidens 



P.moturus 



2.05 lAb 2.S5 3.25 

 LENGTH Mz,PAROM0MYS 



Figure 3.— Histograms illustrative of Cabrera's law as applied to the Gidley Quarry fauna: a. Length 

 of Ml in hyopsodcntids: in this and some other measurements the species nearly or quite intergrade, 

 and they lived in the same place at the same time, but they are morphologically very distinct and belong 

 to four different genera; b, length of M2 in Paromomys: the two species are morphologically similar, 

 probably are congeneric, and are found together, but in this dimension and in many other characters 

 they do not intergrade. 



M. provocafor 



A.O 4.3 4.6 4.9 5.2 5.5 5.8 6.1 



Length Ma 



Quarry Specimens. 



Of her Upper Lebo Specimens. 



One specimen in each sample. 



4.0 4.3 A.Q 4.9 5.2 

 WIDTH M2. 



Figure 4. — Histogram of measurements of second lower molars of all Lebo specimens of Metachriacus. 

 The distributions of these measurements, which are distributed much as are most of the characters of 

 the samples, are clearly bimodal, and two entities are shown to be present. These entities intergrade, 

 but they are separated by provenience, the two coming from different horizons and localities within the 

 Lebo. They are thus interpreted as closely allied but separable species. If they occurred together, a 

 more probable interpretation would bo that they represent the two sexes of a single species. 



