The mandible of the Atlantic City specimen of _M. europæus_ resembles
that of the type, as figured by Van Beneden and Gervais, in the shortness
of the symphysis and in the position of the tooth, which is in advance of
the posterior end of the symphysis. A number of differences, however,
require consideration. (Pl. 11, figs. 3 and 6.)
In the type, the symphysis, as shown by Van Beneden and Gervais’ figure,
plate 24, fig. 2_a_, is a little more than one-fifth the length of the
mandible. The same relative proportion is found in the Atlantic City
specimen, but, as the latter is a younger individual, one would expect
the symphysis to be shorter. The figure of Van Beneden and Gervais gives
the impression that in the type the end of the mandible is broken, and
that, hence, the symphysis is shorter than it was originally. It will be
observed that figures 2 and 2_a_ do not agree as regards the length
between the tooth and the end of the jaw, figure 2_a_ showing a greater
length. In figure 2, however, the jaw seems rather too long for the
cranium, and if the greater length of the symphysis shown in figure 2_a_
were introduced, it would certainly be so. The explanation of this
discrepancy is not readily found; but one may be allowed to think that
the symphysis is not so blunt in the type as is shown in figure 2.
In the Atlantic City specimen the superior lateral free margin of the
symphysis is straight, while in the type it is much elevated. This is no
doubt due to difference in age and possibly in sex. The type shows three
or four mental foramina, while the Atlantic City specimen has one large
posterior one and seven smaller ones anterior to it.
Another peculiarity of the latter specimen is that the coronoid process
is situated much in advance of the condyle, while the angle extends
considerably behind it. In the type both are nearly in line with the
condyle. I am unable to explain this difference.
In the Atlantic City specimen the axis of the tooth where it emerges from
the alveolus is 91 mm. from the end of the jaw. The portion of the tooth
above the alveolus is 11 mm. long at the base and 12 mm. high. It is
conical and sharp pointed, and is inclined forward and a little outward,
especially at the tip. At the alveolus the transverse breadth of the
tooth is 5 mm. The much larger tooth in the type indicates that that
specimen was a male.
The mandible of the Atlantic City specimen of _M. europæus_ differs from
that of _M. bidens_ in the relative shortness of the symphysis, the large
number of mental foramina, the more anterior position of the tooth, and
the direction of the crown, which is forward instead of backward.
_Dimensions of the type and two other skulls of Mesoplodon europæus._
Column headings:
A: English Channel, type,[a] adult.
B: North Long Branch, New Jersey, female, adult.
C: Atlantic City, New Jersey, 23346 U.S.N.M., male, young.
Measurements. A B C
mm. mm. mm.
Total length 762 ([b]) 675
Length of rostrum 459 ... 427
Tip of beak to posterior end of pterygoids 561 ... 525
Height from vertex to end of pterygoids [c]292? 283 256
Breadth between orbits 327 [d]325 [d]287
Breadth between zygomatic processes 360 [e]325 302
Breadth at anteorbital notches 210 205 [f]182
Breadth of beak at middle 66 ... 60
Depth of beak at middle 54 ... 40
Greatest breadth of premaxillæ proximally 168 147 142
The same, in front of anterior nares 111 99 104
Breadth of anterior nares 51 45 42
Length of temporal fossæ 102 115 101
Breadth between temporal fossæ 228 212 208
Breadth of foramen magnum 42 34 34
Length of mandible 654 ... 565
Length of symphysis 135 ... 116
Greatest depth of mandible 120 ... 101
[a] Dimensions taken from Van Beneden and Gervais’ figures.
[b] Beak lacking. Length from occipital condyles to base of beak
(straight), 312 mm.
[c] Pterygoids broken.
[d] At middle.
[e] Estimated. One zygoma is broken.
[f] Least.