Description of a New Rodent. 



75 



some of the smaller bats. Near the base of the auricle on the inner side 



are three well developed cross-ridges, and a fourth which is less distinct, 

 Skull. — Th* skull (fig. 18) is in general similar to that of Idiurus :< nh ri. 



The bony palate, however, is 



at its widest point scarcely 



wider than the first molar, 



while at its narrowest point it 



is decidedly narrower than this 



tooth. In I. zenkeri the palate 



is about double as wide as the 



tooth row.* Surface of frontals 



slightly and evenly convex, 



with scarcely a trace of the 



six protuberances mentioned 



in the description of /. zenkeri ; 



orbital edges knifedike and 



slightly overhanging. Incis- 

 ive foramen a narrow slit, 1 



mm. long and about one-third 



as wide. 



Mandible very short and 



deep, the greatest depth con- 

 tained only one and one-half 



times in greatest length. Cor- 



onoid process joined with artic- 

 ular process by a thick bridge FlG - Ls -~ Skull of Idiurus macrotis. (X 1%). 



below which the bone is thin and semitransparent, but not fenestrate as 



in the type of /. zenh ri.j 



Teelh. -Upper molar rows slightly convergent anteriorly. Combined 

 iength of three true- molars equal to anteropos- 

 terior diameter of incisor. Premolar about three- 

 fourths as large as first molar, which is the lamest 

 upper tooth. Second molar distinctly smaller 

 than first and about twice as large as third. The 

 crowns of the premolars and the first and second 

 c3dJ>/' 7 molars are each crossed by two ridges of enamel, 

 isolating three narrow depressions, the posterior 

 of which is so narrow as to be practically invisible 

 to the unaided eye (fig. 19, a). Third molar with 

 one ridge and two depressions in the type, two 

 ridges and three depressions in an older specimen 



with very much worn teeth. 



First and second lower molars (tig. 19, b.) essentially equal in size, but 



second slightly the larger. Third molar considerably smaller than second 



Fig. 19.— Teeth of Idiurus 

 macrotis; a upper, b 

 lower. (X1%.) 



* " Gaumenbein fast doppelt so breit wie die Zahnreihe . . ." 

 t The fenestration in /. zenkeri may be due to injury during prepara- 

 tion of the specimen. 



