PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 79 
navigation” of Bering Island will show you likewise’some of the ways 
in which these skeletons are deposited, preserved, and found. 
At this place I shall present only a few remarks, occasioned by the 
inspection of the 11 skulls which I have obtained, and the two belong- 
ing to Dr. B. Dybowski, now in Petropaulski. 
It is obvious at first sight, when comparing this series, that a remark- 
able individual variation is shown by each one of these skulls. Setting 
aside the differences caused by the more or less perfect state of pres- 
ervation, these variations especially embrace the more or less marked 
developments of the lines, crests, protuberances, and processes for mus- 
cular insertion, and the more or less robust formation of special parts. 
Although the skulls are of about the same size, these differences, I 
think, are due to age, as it is very probable that these large animals 
must have reached an almost patriarchal age, and that the development 
of the bones in consequence hereof has been proportionally slow, con- 
tinuing even after the skull had obtained the full and final size. 
But, besides these individual variations, there is another striking dif- 
ference, which divides the series into two well-defined groups. Dr. 
Dybowski and I stood side by side, looking at several skulls before us, 
aud I had no sooner perceived and showed to him this fact than he 
was impressed in the same manner. We now eagerly sought for con- 
firmation in the other skulls, and as we, by a careful examination, found 
a no less marked difference in the shape of the lower jaw, we brought 
together a tolerably good collection of these bones, commencing an ex- 
haustive series of measurements to serve as a foundation for and proof 
of our discovery.* I have given below two tables containing the more 
interesting of these measurements. 
The idea of two different species or varieties of the sea-cow was very 
soon rejected, and without much hesitation we agreed that the differ- 
ence is a sexual one. This seems to be the only reasonable solution, 
and, judging from analogy we think that the broader and more robust 
skull belongs to the male, while the narrower and more slender one is 
that of the female, a supposition corroborating the opinion of the natives, 
who also have been aware of the difference. Of this, however, we were 
not informed until much later, when we made inquiries about the mat- 
ter; but we could not learn whether this assumption is founded on tra- 
ditions from the time when these animals still occurred in the surround- 
ing waters or not. 
*T call it thus because I doubt whether asimilar observation has been published by - 
any one before. This is, maybe, somewhat daring, considering our want of liter- 
ature, but I prefer to take this risk rather than to wait until next year, and perhaps 
come too late with ‘‘ the discovery.” 
