LÖNNBERG, STUDY OF THE VARIATION OF EUROPEAN BEAVERS. 9 



much larger t han the width across the postorbital processes. 

 In the Elbe Beavers, on the other hand, the latter measure- 

 ment is larger than the former which is absolutely somewhat 

 smaller than the corresponding dimension of the fully adult 

 Moldavia-Danube Beavers. The postorbital processes of the 

 Elbe Beavers are comparatively very well developed and this 

 is also the case with the frontal processes of the zygomatic 

 arch. The shortest distance between the postorbital process 

 and the frontal process of the zygomatic arch measures there- 

 fore in the Elbe Beavers about 19 mm. but in the Moldavia- 

 Danube Beavers about 24—26 mm. This difference does not 

 appear to be due to difference in age between the compared 

 specimens but it may to some extent be increased by differ- 

 ence in sex as the longest and oldest Danube specimen is 

 a female with little developed frontal process of the zygo- 

 matic arch, while the large Elbe specimens as already stated 

 are old males. In the Elbe Beavers the distance between the 

 base of the postorbital process and the suture between the 

 lacrymale and the frontal is contained fully twice in the 

 distance between the tips of the postorbital processes, but in 

 the Moldavia-Danube-Beavers the former distance is about 

 two thirds of the latter or even more. This stånds of course 

 in connection with the greater or less development of the 

 postorbital processes. 



Matschie writes in his paper quoted (p. 219) about his 

 »Castor albiciis» that the greatest zygomatic width is »nur 

 sehr wenig grösser» than the distance between the tips of the 

 nasals and the sutiira coronalis. In the two large Elbe Bea- 

 vers as well as in the specimens from Moldavia and Danube 

 the zygomatic width is much the larger measurement. The 

 same is also the case in Swedish Beavers. 



The basioccipital groove is a little shorter and compara- 

 tively broader in the Moldavia-Danube Beavers than in the 

 old Elbe Beavers. The apparent broadness of the former is, 

 however, partly due to the fact that the lateral walls of the 

 basioccipital groove are not so high nor curved inwards as 

 in the Elbe Beavers. This may, however, to some extent 

 depend upon difference in age and sex as the walls of this 

 groove become higher with increasing age. 



Matschie has used as a distinguishing characteristic the 

 dimensions of the nasal opening, vertical height in the middle 



