ALLEN : MAMMALIA : OCTODONTID/e. 39 



palatal length, 25; diastema, 16; upper molar series, 9.6; lower jaw, inner 

 base of incisors to posterior border of condyle, 33 ; inner base of incisors 

 to tip of angular process, 41 ; height at condyle, 16; lower molar series, 

 10.3; distance between condyles, 18; distance between tips of angular 

 processes, 37. Ten adult male skulls: Total length, 53.6 (51-55) ; zygo- 

 matic breadth, 30.5 (29-33). Five adult female skulls: Total length, 48 

 (46-50) ; zygomatic breadth, 27.5 (26.2-28.6). The mastoid breadth is 

 practically the same as the zygomatic breadth, varying in different speci- 

 mens from slightly more to slightly less. The greater part of the skulls 

 in the present series are middle-aged, with all the sutures distinct ; only 

 two or three give evidence of being very old. 



Represented by 23 specimens, all from the upper Rio Chico, Cordilleras, 

 and all collected by Mr. Peterson, February 7 to 28, and one March 6. All 

 but three are in adult pelage, and these have nearly acquired it, only 

 the lower part of the back and rump retaining the pelage characteristic of 

 immaturity. The general color above of the adults varies from strong 

 yellowish brown to slightly rufescent brown, and below from deep ochra- 

 ceous buff to brownish ochraceous. The color of the tail is very variable, 

 as already noted ; except in the case of a few^ which have the tail practically 

 uniform yellowish gray, no two have the tail colored alike, in respect to the 

 median dorsal line, which varies from a slight trace of dusky to a well 

 defined blackish median stripe, the black widening and increasing in 

 intensity apically ; in three specimens the whole tip of the tail is black, 

 including the under surface, two of which are males and the other a 

 female. A few other specimens approach this condition. 



As shown by the measurements already given, the females are very 

 much smaller than the males. 



The skull is very variable in respect to size and many details of struc- 

 ture, but especially in the size and form of the interparietal. In one 

 specimen it is almost obsolete, forming a mere line less than a millimeter 

 in antero-posterior extent and 5 mm. in transverse extent. Generally it 

 is subtriangular, with a transverse width of 5-7 mm., and an antero-pos- 

 terior length of 2-4 mm. It is sometimes divided medially into two 

 halves. On each side of the interparietal, and separated from it by the pos- 

 terior extension of the parietals, is an intercalated bone of variable size 

 and of an irregularly oval front outline, each generally considerably larger 

 in area than the interparietal. 



