PROCEEDINGS OF UNITED STATES NATIONAL MUSEUM. 83 
in the male is equal to or less than the distance between the angles, 
while it is greater in the female. 
How closely the posterior angles approximate to each other in the 
female as compared with the male, is clearly expressed by the average 
figures of this distance and of that between the condyles. While the 
difference between the figures of the latter only amounts to 1Li™ it 
is in the former distance, which is not more than about one-half of the 
other, not less than 48"" or in other words: The difference between 
the average distances of the condyles amounts to about 5 per cent. of 
the smaller dimension, while the difference between the average dis- 
tances of the angles is 44 per cent. 
The average measurements furnish us with still more distinguishing 
marks. Thus, in the male the distance between the posterior angles is 
more than one-third of the total length of the horizontal ramus, while it 
amoutits to almost exactly one-fourth in the female. Besides, the for- 
mer distance in the male is greater than the smallest breadth of the 
vertical ramus, while the reverse is true in the other sex. 
It may be well to give here the measurements of two other mandibles, 
which were not included in the above table, the one (No. 1202) a very 
young male, the dimensions of which would have diminished the aver- 
age measurements so as tg obscure the results, while the other (No. 
1636), an adult female, was only found after the table had been com- 
piled, when the other jaws were packed and shipped. 
The numbers of the dimensions correspond with those of the table 
above: 
whi. | | | ase 
Collector's No. | Sex| ae! | ei a, | | 6 | 7. | 8 
Typ aD) PREG pare pes 
|mm. | mm. | mm. mm. mm.|mm.| mm. mm. 
STEP ELON Der o0 le ome cen mae ame cess anise «loo « fol 380 | 245 | 247 | 155 | 84) 104 | 224) 122 
Stejneger No. 1636....-.............. ewes See | g 437 | 288] 303 | 197] 99] 121) 2382) 112 
| 
It is interesting to see how closely the dimensions of the female jaw 
approximate the average dimensions of the table, and consequently how 
well they agree with the diagnosis. In the young male the proportions 
are a little obscured, as the bone has not yet assumed its final shape. 
The characters of the male jaw, however, are pretty well marked. The 
outward direction of the posterior angle is especially characteristic. 
Concerning the year of the final extinction of the sea-cow I have little 
doubt that von Baer and Brandt, in supposing it to be 1768, are very 
nearly correct. That a single individual or two, perhaps, may have 
survived the others a few years is not impossible, but it is almost cer- 
tain that such a huge animal, bound to the very coast for its subsist- 
ence, hardly could have found a place in which to hide itself from the 
keen eyes of its pursuers, who were sufliciently numerous and greedy 
to search for and slay even the last one. Besides, the animal does not 
seem to have avoided its enemies, a want of intelligence which in a 
