68 



MR. E. R. ALSTON ON THE ORDER GLIRES. [Jan. 18, 



drical, either covered with scales arranged in rings, or more or less 

 hairy. The Myomorpha contains such a variety of forms, many of 

 them much specialized, that it is only by allowing for exceptions 

 that its definition can be carried further ; still many and important 

 distinctions are common to the vast majority. The form of the man- 

 dible, by which the section was first separated from the Hystrico- 

 morpha, agrees with the last section, the angular portion springing 

 from the lower edge of the bony covering of the lower incisor, 

 excepting in the subfamily Bathyergince, in which it has exactly the 

 form so characteristic of the hystricine rodents. The other cranial 

 characters are very varied. In the more typical forms the infra- 

 orbital opening has a peculiar shape, which may be termed murine ; 

 it is high, perpendicular, narrow, wider above than below ; and the 

 lower root of the maxillary zygomatic process is perpendicular and 

 flattened into a thin plate with a rounded anterior edge. The zygoma 

 is comparatively slender ; the malar seldom advances far forward 

 (except in the Dipodidce), and is usually supported below by a con- 

 tinuation backwards of the maxillary process, being reduced in some 



Fig. 3. 



Mandible of Bathyeryus ■maritimus. 



of the typical genera to a mere splint between the latter and the 

 squamosal process. The outer walls of the pterygoid fossae are gene- 

 rally obsolete ; and they have no direct fissure at the bottom, except 

 in the aberrant subfamily named above. The clavicles are perfect 

 except in the Lophiomyidce. 



