234 



PROCEEDINGS OF TTTR ACADEMY OF 



[1894. 



curved strongly upward and inward; angle produced backward 

 liehind plane of condyle, and strongly inflected ; ramus of mandible 

 thickened opposite molar teeth and abruptly narrowed and beveled 

 to incisors. 



The principal characters that separate Hodomys from Xenomys are 

 arranged antithetically in the following table: — 



XENOMYS. 



Posterior part of mandible 

 only moderately expanded, short 

 and cut away by deepening 

 of coronoid and infracondylar 

 notches (particularly the latter). 



Angular process decidedly an- 

 terior to plane of condyle. 



Condyle overtopping coronoid. 



Anterior root of coronoid cut- 

 ting plane of posterior loop of 

 m 2 ■ 



Horizontal ramus nearly 

 straight below molar series. 



Cranium short. 



Squamosal not reaching supra- 

 occipital. 



Audital bulht' enormously in- 

 flated, wheel- shaped, parallel, 

 broadest anteriorly. 



Audital bullie much longer 

 than molar series and covering 

 more than two-thirds distance 

 from foramen magnum to post- 

 palatal notch. 



Carotid canal inconspicuous, 

 far behind middle of bulla. 



Orbital borders of frontals 

 produced laterally, forming a 

 shelf- like bead over orbits. 



HODOMYS. 

 Posterior part of 



long. 



mandible 

 large, and broadly ex- 

 panded posteriorly; coronoid and 

 infracondylar notches relatively 

 shallow^ 



Angular process produced 

 backward behind plane of con- 

 dyle. 



Coronoid overtopping condyle. 



Anterior root of coronoid cut- 

 ting plane of anterior loop of 

 m 3- 



Horizontal ramus decidedly 

 convex downward below molar 

 series. 



Cranium long and narrow. 



Squamosal articulating unth 

 supraoccipital. 



Audital bullae very small, 

 subfusiform, abruptly narrowed 

 anteriorly and produced ob- 

 liquely forward toward median 

 line. 



Audital bullic much shorter 

 than molar series and covering 

 only about one-third distance 

 from foramen magnum to post- 

 palatal notch. 



Carotid canal conspicuous, 

 anterior to middle of bulla. 



Orbital borders of frontals 

 upturned, not projecting over 

 orbits. 



