30 ARKIV FÖR ZOOLOGI. BAND 8. N.O 10. 



A. taczanowskii has according to Stolzmann a short and broad 

 skull so that its breadth is contained only 1,38 times in its 

 length, while in the typical Paca the relation is 1,50. This 

 alpine Paca again has a narrow skull, the breadth of which 

 is contained about 1,59 times. in its length. Another diffe- 

 rence from several other races of Paca is that in spite of the 

 age of this alpine specimen there is no crista sagittalis deve- 

 loped on its skull, the areas of musculi temporales not even 

 meeting behind at the lambdoid crest. The molar series are 

 converging in front, so that the width of the palate opposite 

 the middle of the premolars is about 7 mm, while it is 11,5 

 mm at the middle of the last molar. 



The shape and the dimensions of the nasals are also very 

 different from the corresponding ones of A. taczanowskii. 

 In the latter they are very short so that their combined breadth 

 is only contained l l f 2 times in their length, while in the alpine 

 Paca the breadth of the nasals is contained fully two times 

 in their length. In the alpine Paca the length of the nasals 

 is even a little more than the mesial length of the frontals. 

 The latter bones are quite smooth without any pits or rugo- 

 sities. 



Foramen infraorbitale is very large measuring 36 mm in 

 length, and 19 in height, the latter dimension being even 

 somewhat greater than that of A. taczanowskii. 



The upper incisors of the alpine Paca have a quite flat 

 anterior surface so that the cutting edge consequently be- 

 comes quite straight and transverse. This is quite different 

 from the condition found in the Brazilian Paca in which the 

 anterior surface of the incisors is strongly convex, and thus 

 the cutting edge curved. The lower incisors are a little more 

 convex on their anterior surface, but by far not in such a high 

 degree as in the Brazilian Paca. 



The coronoid process of the lower jaw is very little deve- 

 loped, and very much smaller than in the Brazilian Paca. 



A. sierrce an- 

 dina c? ad. 



Greatest length of skull 122 mm 



Condylo-incisive length 115,5 » 



Basicranial length (to tip of premaxillaries) . . . . 113,5 » 



» » (Hensel) 100 » 



Greatest zygomatic width 76 5 » 



