Cope. 



454 



l Feb. 6. 



by the presence of the subsquamosal, but in Hypsiprymnus and Macropus 

 this foramen becomes the postsquamosal, through the failure of the post- 

 zygomatic crest. It need not be confounded with another foramen also 

 found in these genera, which enters above the meatus auditorius externus, 

 and communicates with the tympanic chamber, and which I call the su- 

 pratympanic foramen. The subsquamosal enters the sinous canal, and in 

 PJiascolarctos, where the postglenoid is wanting, constitutes its only exter- 

 nal outlet. The order is further characterized by the presence of the post- 

 zygomatic foramen. 



Phaxcolomys ; postzygomatic chamber enormous, extending above mea- 

 tus. No foramina below, except supratympanic ; above, a supraglenoid 

 and one or two postglenoids. 



Phascolarctos ; subsquamosal and postzygomatic only ; the latter com- 

 municating with an empty chamber. 



Macropus and Hypsiprymnus ; postglenoid, postzygomatic, supratym- 

 panic and postsquamosal ; the second communicating with a chamber filled 

 with cancelli. 



Fig. 1. — Skull of opossum ( Didelph.r/s virginiana) natural size, posterior view, 

 parts of the right mastoid and squamosal bones removed. M, mastoid fora- 

 men ; SBS, subsquamosal ; PG, postglenoid; PZ, postzygomatic foramen. 



Didelphys ; postglenoid, postzygomatic, subsquamosal and mastoid ; 

 postzygomatic small. 



Dasyurus; postglenoid, subsquamosal and probably mastoid. I cannot 

 find a postzygomatic. 



Phalangista ; postsquamosal and postparictal only ; no postzygomatic 

 nor supratympanic. 



Edentata. 



Tamandua ; F. f. diploetica anterior and posterior, and postsquamosal 

 only. 



Dasypus (6-cincius) ; postglenoid (large), postsquamosal, mastoid, 

 several postparietals, and a small subsquamosal. 



