12 



ARKIV FÖR ZOOLOGI. BAND 5. NIO 0. 



in the molars the end of the inner fold is more or less coni- 

 pletely opposite to that of the antero-external fold, as Mat- 

 SCHIE regards typical for Elbe-Beavers. In m^ the inner 

 fold is short, in the others it reaches across aboiit half the 

 surface of the crown. In p^ of both sides, however, the 

 inner fold extends between the ends of the middle and an- 

 terior outer folds. 



In the Beaver from Danube at Ulm the condition is 

 more aberrant. In m'^ of the left side the pattern is similar 

 to Matschie's Elbe-type, so to say. In m^ of the left side 

 the posterior external fold has been detached from the outer 

 enamei covering so that it appears on the worn surface as 

 a short transverse fold completely separate from the surroun- 

 ding enamei layers. The middle outer fold is very long but 

 the antero-external fold is entirely absent. The inner fold 

 is well developed. The enamei pattern of m^ is still more 

 reduced as not only the anterior but also the posterior outer 

 fold is wanting. There are thus only the inner and the 

 middle outer fold left. In 2^^ the posterior outer fold is fully 

 detached as in m-. The other folds are normal and the inner 

 fold ends free between the middle and anterior outer folds. 



On the right side (fig. 4) m^ is 

 normal and shows the »Elbe- 

 type» in the ärran gement of 

 the enamei folds. In m^ the 

 posterior outer fold is fully de- 

 tached as on the left side and 

 the antero-external fold is re- 

 p^ to the left of^the fig., m^ to the presented by a tiny enamei 



ring only. In m^ the posterior 

 outer fold is detached as in m^ but the anterior outer 

 fold is entirely absent. In p^ the posterior outer fold 

 has disappeared, and the antero-external is fully detached. 

 It is thus evident that on the whole a considerable reduction ^ 

 of the enamei pattern has taken place in this Beaver, but 



Fig. 4. Right upper molar series 

 of an adult Beaver $ from Danube 

 at Ulm (inner side up on the fig., 



^ It is more than probable that these elements, which now are lacking, 

 have been present when the animal was younger, and have been worn off, 

 but, nevertheless, it is quite correct to speak about a reduction of the 

 enamei as the skull proves to have belonged to a not very old animal with 

 open sutures. As the enamei pattern normally is complete in much older 

 animals than this one it is clear that the specimen in question has been 

 subjected to a reduction with regard to its enamei. 



