6 ARKIV FÖR ZOOLOGI. BAND 5. N:0 6. 



In a quite young Swedish Beaver the palatal width between 

 the premolars amounts to 8 mm., in the adult ones it is 

 about 7 mm. and in the oldest hardly more than 4 mm. It 

 is thus no distinguishing characteristic when in two large Elbe 

 Beavers the same dimension measures resp. 5,5 and 6 mm. 



There seems, however, to be some slight differenees 

 between the Swedish Beaver and the Elbe Beaver which 

 appear to be constant as far as the available material is con- 

 cerned. In the latter the premaxillary portion below the 

 alveoles of the incisors are more strongly constricted than in 

 the former. There is thus a broad and very conspicuous 

 concavity formed in the Elbe Beaver behind and below the 

 elevation of the surface caused by the alveoles of the incisors, 

 while in the Swedish Beaver the lateral siirfaces of the pre- 

 maxillaries slope more evenly from the alveolar elevations 

 towards the palatal surface and the concavity is very slight 

 if any. This characteristic holds good in young as well as 

 iu old specimens which I ha ve examined. In the Swedish 

 Beaver the suture between the premaxillary and the nasal 

 slopes evenly downward all the time to the nasal opening so 

 that the upper contour of the premaxillary is straight when 

 viewed from the side, but in the Elbe Beaver it assumes a 

 horizontal course or even turns a little upwards about a 

 centimeter from the nasal opening, and in any case the upper 

 contour of the premaxillary is plainly concave. This pro- 

 duces a somewhat different shape of the nasals so that their 

 greatest combined width in large Elbe Beavers is about 

 5 mm, broader than the combined width at the nasal opening, 

 while the same difference in Swedish Beavers is 3,5 to 4 mm. 



In one of the large Elbe specimens the nasals are rather 

 highly vaulted but in the other it is just as flat as in any 

 Swedish specimen. This proves that the shape of the nasals 

 as well is subject to variation. 



As Matschie in his paper quoted had created not only 

 a new »species» for the Elbe Beaver but two more viz. 

 »Castor balticus» based on a skull from Dölitz in Pomerania, ^ 

 and »Castor vistulanus» on a specimen from the western parts 

 of Poland, it interested me to examine some more specimens 

 of Beaver from different parts of Europé. Thanks to the 



^ With which a broken skull from Holstein is said to agree. 



