114 



BULLETIN 169, UNITED STATES NATIONAL MUSEUM 



The dimensions of the type are as follows: Length P4, 1.4; width 

 P4, 1.0; length M„ 1.5; width Mj, 1.2; length M2, 1.4; width M2, 1.3; 

 length M3, 1.5; width M3, 1.1. 



The available numerical data on the whole sample are given in 

 table 24. 



Table 24. — Numerical data on specimens of Leptaeodon ladae 



The two available specimens of L. tener are at or slightly below 

 the observed lower limits for L. ladae in all molar dimensions. The 

 deviations of the four available dimensions of the type of L. tener 

 from the means of L. ladae, divided by the corresponding standard 

 deviations of the latter (d/a) are as follows: 



LMi:-6.1 

 WMi :- 5.0 



LM2:-4.0 

 WM,:-2.9 



The size difference, slight as it is, thus appears to be significant. 

 Individual measurements of L. packi are not available, but that 

 species is very close to L. tener in size, hence probably also signifi- 

 cantly smaller than L. ladae. 



LEPTACODON MUNUSCULUM Simpson 



Figure 16 



Leptaeodon munusculum Simpson, 1935d, p. 228. 



Type.— U.S. ISIM. no. 9819, left lower jaw with Mi and M3. Col- 

 lected by A. C. Silberling. 



Horizon and locality. — Gidley Quarry, Fort Union, Middle Paleo- 

 cene horizon, Crazy Mountain Field, Mont. 



Diagnosis. — Mj of about the same size as in L. tener, M3 more 

 reduced. ^^ Paraconids smaller and more strictly internal. Talonid 

 of M3 relatively narrower. 



Remarks. — This poorly known species is the smallest mammal in 

 the collection and is one of the smallest mammals known. It is 



•3 The original diagnosis says "Slightly smaller than Leptaeodon tener", which was probably true of 

 the dentition as a whole and perhaps of the animal, but Mi is as large as in L. tener. 



