176 BULLETIN UNITED STATES GEOLOGICAL SURVEY. [Vol.YI. 



M. 



Diameters of premolar (i) 5 antero-posterior 014 



( transverse 009 



Length, of last three premolars on base (No. 2) 034 



Length of base of fourth premolar Oil 



Length of base of first true molar • .019 



Length of first diastema (No. 2) 017 



Length of second diastema (No. 1) 026 



Depth at second diastema (No. 1) 033 



Depth at first true molar 048 



The generic position of this species is uncertain. I place it provis- 

 ionally in Protolabis on account of the large development of the infe- 

 rior incisors. Its robust canine and first premolar, and small third and 

 fourth premolar distinguish it from any of the species described. 



Found by E. H. Hazard, in the Loup Fork beds of Southern E'e- 

 braska. 



EXBITS LOCKINGTONIANUS Sp. nOV. 



This rodent is represented by a nearly perfect skull, which is without 

 lower jaw. Its specific characters separate it widely from the E. elegans 

 Leidy and E. nematodon Cope. It is considerably larger than either, 

 and the temporal ridges are very obsolete and do not unite posterior 

 to the orbits, as in U. elegans, resembling in this respect the U. nemato- 

 don. The parietal region is wide and flat above. The interorbital region; 

 is only moderately contracted. The muzzle is rather short as compared 

 with the total length of the skull. The interorbital region is gently 

 convex above, and the top of the muzzle is flat. The zygoma is quite 

 slender, and the otic bullse are large and prominent. The notch of the 

 palate extends as far forwards as the posterior part of the last superior 

 molar. The infraorbital foramen is very large and round. 



The anterior face of the superior incisor is nearly plane, and it is 

 marked by a weak groov^e near the inner and a strong groove near the 

 external border. In U. elegans this face is convex and without grooves. 

 The molars are rather small for the size of the skull ; their crowns are 

 worn by use. The third is subround in section, and its diameter is about 

 half that of the first; the latter has the anterior odd lobe quite small. 



Measurements. 



M. 



Total length of skuU 0380 



Length (axial) to front of orbits 0140 



Length (axial) to palatal notch , 0190 



Length (axial) to first molar..., 0120 



Width at otic bullae 0205 



Width at middle of zygomata 0220 



Width of interorbital space 0060 



Width bet^veen first molars 0055 



Length of molar series 0070 



Length of first molar 0030 ^ 



Width of superior incisor 0015 



This species is dedicated to my friend W. N. Lockington, the well- 

 known naturalist of San Francisco. 



