360 U. Ss. P. R. R. EXP. AND SURVEYS—ZOOLOGY—GENERAL REPORT. 
beaver, and in them discusses at great length the question of the relationships of these animals 
in the two worlds. He sums up the evidence on the subject as follows: 
1st. The external distinctive marks given by Kuhl, Oken, and others, have no real value in 
showing a difference of species. 
2d. The size of the American beaver is not essentially, if at all, greater than that of the 
Kuropean. 
3d. No distinctive characters between the two have yet been detected in the formation and 
structure of the head, ear, feet, and tail. 
4th. A comparison of eight European with five American beaver skulls shows very decided 
distinctive characters between the two. 
5th. Many of these differences in the skull involve variations in external form. 
6th. The established difference between the two in the castoreum bag and its secretion 
furnish strong grounds of specific distinction. 
In reference to the comparative sizes of the beavers of the two worlds, it is quite evident that 
Brandt has not known the largest of our beavers in the skulls before him. Thus, the largest 
European skull he had observed measured 5.60 inches by 3.91, reducing his scale of French 
inches to English ; the largest American measured 5.24 inches by 3.60. From the accompanying 
table of measurements of skulls of American beavers in the Smithsonian collection, it will be 
seen that the largest measures 5.80 by 4.16 inches, (dimensions taken with callipers,) and that 
nearly half of them exceed the size given by Brandt. The largest measurements given of the 
Polish beaver amount to about 34 inches for the head and body, and 11 inches for the tail. 
These, if French, would be 36.23 inches for the one, and 11.72 for the other. The largest skin 
measured of the Smithsonian collection gives to root of tail 35 inches, length of tail. 11 inches, 
width of tail 5} inches, length of hind foot 6 inches. I have, however, seen others very appre- 
ciably larger ; and this specimen was not stuffed out at all, but the skin was perfectly flat. 
It will thus be seen that the largest beaver skull recorded thus far is an American one, thus 
inclining the balance of size in favor of our species. The largest weight I have known of an 
American beaver was of 56 and 60 pounds, as given by Dr. Hayden ; he is, however, confident 
that he has seen them still larger. The heaviest Old World beaver on record is one of 50 
pounds, mentioned by Pallas. Brandt suggests that this is the smaller Russian pound ; its 
ratio to the English pound I am unable to state. 
The differences of the skull are, to a certain extent, such as have already been referred to, 
although our author does not find the difference in the upper outline of the head, the malar bone, 
and the portion enclosing the brain, mentioned by Cuvier. The most constant and quite appre- 
ciable difference was in the character of the nasal bones, which, in all European specimens, 
measure considerably more than one-third of the distance from the incisors to the crista occipi- 
talis, while in the American they are little, if at all, over one-third this length. The backward 
projection of the nasals is therefore much greater in the European animal. Many other less 
appreciable differences are indicated in Dr. Brandt’s elaborate article. 
An appreciable difference in the castoreum bag of the two animals is mentioned by Brandt. In 
the American beaver, this is more elongated and less thick skinned than in the European. The 
castoreum itself also is not only less in volume, but when long exposed to the air, or kept a good 
while, assumes a more or less lustrous amber-like appearance, not wax-like and lustreless as in 
the European. In this secretion of the European animal there is much the largest proportion 
of ‘‘etherial oil, castorine, and castoreum-resinoid.’’ 
