204 Bulletin American Museum of Natural History. [Vol. XIX, 



indications of a large alveolus lead to the suspicion that one 

 or more of the incisors was enlarged. 



No. 9612, part of a lower jaw with the roots of the last two 

 molars, is also referred here. 



This remarkable little jaw is quite unlike any described 

 species of Insectivore or Chiropter, except, perhaps, Marsh's 

 Centracodon. So far as anything can be determined from his 

 brief description, the last molar of Centracodon is like the 

 second molar of Apternodus . Centracodon has four premolars. 

 Although the short, deep jaw would appear to ally it rather 

 with the Chiroptera, yet as the tooth without talonid is quite 

 unknown in this order, while it does characterize a section of 

 the Insectivora, I leave it provisionally in the latter group, 

 without attempting to assign it to any especial family. Its 

 nearest relatives are most probably the little Eocene Insec- 

 tivora from the Bridger Basin, described by Professor Marsh 

 in 1872. AVith the probable exception of these Eocene types 

 and of a single South American species, no fossil Insectivores 

 of the Z^alambdodont division have hitherto been described, 

 although according to the Tritubercular theory this, as the 

 more primitive section, should have been more abundant 

 in ancient times. 



Measurem ents. 



M2-3 3-9 T^™-- 



M2 longit 2.0 



" transv 2.0 



" height 3.7 



M3 longit 2.0 



" transv 1.8 



" height 2.9 



Depth of jaw 3.5 



Micropternodus borealis, gen. et spec, no v. 



Type, No. 9602, a lower jaw with P3_ni3 and alveoli of the anterior 

 teeth. 



Dentition sTi^i. Molars somewhat like those of Centetes in corwpo- 

 sition, with high trigonid and small, low talonid. Trigonid very wide 

 transversely with pr'* considerably overtopping pa'^ and me*^- Talonid 

 with sharp posterior margin and low median ridge. Molars and 

 especially premolars, short, high, and recurved; p4 sub-molariform.with 



