138 Bulletin American Museum of Natural History. [Vol. XX.] 



Doubtless other cases are on record, but those above cited 

 indicate that this structure occurs in several widely separated 

 groups of Rodents. 



In species in which this structure exists, it is not likely to 

 be met with attached to the skull in Museum specimens, 

 since, owing to its nature and position, it would naturally be 

 removed or mutilated by the collector in taking off the skin, 

 attached to which it may doubtless be occasionally detected 

 by careful examination. 



