36 ARKIV FÖR ZOOLOGI. BAND M. N:0 4. 



of the same on the other, to judge from the by Allén in 

 his Monograph published measurements, is rather similar in 

 Simosciuriis stramineiis and certain species of his genus IJro- 

 sciurus. The following compilation may prove this. 



Length of nasals in % of 



tot. 1. of skull interorbital 

 breadth 



Simosciurus stramineiis 27,5 84,2 



Urosciurns igniventris igniventrts .... 30,1 82,6 



» » taedifer ..... 30,1 86,3 



» » zamorae 27,6 85 7 



» pyrrhonotus pyrrhonotus . . . 27,6 81 8 



» langsdorffi langsdorffi .... 29,8 90,6 



» » urucumus .... 32,1 93,3 



» » steinbachi .... 29,0 88,8 



» duida 33,3 110,0 



» tricolor 1 '" \ '' 



129,1 I 97,6 



From the above table may be concluded that the rela- 

 tiva length of the nasals as expressed in pereentages of the 

 total length of the skull and of the interorbital breadth in 

 Simosciurus is fully as great as in certain members of Uro- 

 sciurus, and also that the difference with regard to these 

 pereentages is greater between certain different members of 

 Urosciufus than between such and Simosciurus. In U. tri- 

 color even the individual variation with regard to these dimen- 

 sions is greater than between Simosciurus on one hand and 

 several members of Urosciurus on the other. This charac- 

 teristic is thus not very suitable for the distinction of Allen's 

 two genera mentioned. 



Allén has also in the same Monograph established an- 

 other new genus Hadrosciurus, which is said to be charac- 

 terised by a short rostrum »with short broad nasals, their 

 length about 20 % of the total length of the skull, and abbut 

 66 % of the interorbital breadth» (1. c. p. 265). I regret to 

 say that there appears to be some miscalculation in this 

 case as well. The author quoted states on the next side the 

 average total length of five skulls to be 65,5 mm and the 

 interorbital breadth and length of the nasals of the same to 

 be 23 and 20, i mm resp. The last measurement is then 



