118 



BULLETIN 16 9, UXITED STATES NATIONAL MUSEUM 



Figure l' .—Myrmecoboides montanensis Oidley, U.S.N.M. no. 8037, left lower jaw: a, Crown view; 6, in- 

 ternal view. Four times natural size. 



Figure 18.— Mi/rmecoboides montanensis Gidley, U.S.N.M. no. 9o52, right upper P'-M^, crown view. Four 



times natural size. 



median notch in the external border, and the hypocone more internaL 

 ]\P has the outer portion analogously modified, but this is less dis- 

 tinctive from Prodiacodon than is M^ M^ is of almost identical struc- 

 ture in the two genera. 



Table 25. — Measurements {in mm) of the type and of the referred upper jaw of 

 Myrmecoboides montanensis 



Family NYCTITHERIIDAE Simpson, 1928 



This family was established to include a number of rather poorly 

 known Paleocene and Eocene genera, all represented by species of 

 small or minute size, that probably represent a single varied group 

 and that seem to be primitive shrewlike insectivores, without any of 

 the specializations characteristic of the true shrews. In this respect 

 the dentition is molelike rather than shrewlike, but there is no evi- 

 dence of definitely talpid specializations. As Matthew (1909) has 

 pointed out (in other words), speaking of Eocene genera that I have 

 since placed in this family, they seem to combine all the most primi- 

 tive characters of the moles and the shrews. To this extent the evi- 



