The skull of this Nantucket specimen, which I have before me, is
thoroughly adult. That the specimen is a female is probable from the fact
that the teeth (one of which is preserved), though fully developed, are
only two-thirds as broad and three-fourths as long as those of Sowerby’s
specimen (the type of the species), which was an adult male.[7] The skull
is 765 mm. long, and about 30 mm. are lacking from the end of the beak,
so that the original length was about 795 mm. It appears to be,
therefore, rather the largest skull of the species of which there is any
record. The specimen itself, according to Dr. J. A. Allen, was 16 feet 3
inches long.[8] The largest European skull appears to be the one in the
Edinburgh Museum, described by Sir William Turner in 1872.[9] The length
of this is 749 mm. The specimen was a female, but though the skull is so
large, the mesirostral cartilage was not ossified, and the individual
was, therefore, probably not thoroughly adult. Two other European
specimens, of which the total length was almost identical with that of
the Nantucket specimen, were (1) the adult female obtained at Overstrand,
England, in 1892, and recorded by Southwell and Harmer[10] (length 16
feet 2 inches, straight); (2) the adult male obtained at Brodie House,
Scotland, in 1800, and recorded by Sowerby[11] (length 16 feet). The
length of the skull is not given for either of these specimens. The adult
male obtained at Rugsund, Norway, in 1901, and recorded by Grieg,[12] was
only 15 feet 1 inch long, but some of the measurements of the skull are
as large as, or even a little larger than, those of the Nantucket skull.
The total length of the skull was not given, as the end of the beak was
lacking.
Grieg’s figures of the Rugsund skull afford a very satisfactory basis for
comparisons between that specimen and the Nantucket skull (Pl. 1, fig.
1). Both skulls show the comparatively narrow frontal region, the
moderately developed tubercle anterior to the anteorbital notch, and the
low maxillary ridge, which are characteristic of the species. In both
skulls the anterior prolongation of the ethmoid is lanceolate and flat,
but in the Rugsund skull the apex is truncated. In the latter also the
posterior end of the mesirostral ossification is divided into three
longitudinal sections by two lateral and somewhat divergent grooves,
while in the Nantucket skull there is only a single median groove. These
differences may safely be regarded as individual. Toward the distal end
the surface of the ossification in the Nantucket is pitted and irregular
and descends much below the level of the premaxillæ. It ends distally at
the same point with the vomer. In this skull the proximal end of the
premaxillæ and adjoining plate of the maxillæ are somewhat less reflexed
than in the Rugsund skull. The shape of the superior margin of the
supraoccipital is alike in both.
There are no well-defined differences in the relative thickness of the
beak at the base or in the form and position of the visible portion of
the palatines, but in the Nantucket skull the mass of the combined
frontal and lachrymal anterior to the orbit is less rounded and more
triangular than in the Rugsund skull. The temporal fossæ also have a
postero-superior angular enlargement not seen in the latter.
In the Nantucket skull the rostral portion of the premaxillæ is high and
at the distal end vertical. The superior profile is somewhat convex, and
the superior free margin rounded proximally, but sharp distally. The
least distance between the free margins is 10 mm.
The pterygoids are cut off from the maxillæ anteriorly by a very narrow
band of the palatine, which connects with a broad band externally and a
lanceolate segment internally. The inferior pterygoid ridges diverge
anteriorly. The broad surface internal to them is concave. The external
border of the pterygoid sinus is nearly straight. An elongated, fusiform
section of the vomer is visible on the inferior surface of the beak at
the middle for a distance of 158 mm., and a small lozenge-shaped section,
ill defined, is visible between the pterygoids and palatines. (Pl. 4,
fig. 1.)
The expanded anterior end of the malar is rhomboidal in form, with an
external free margin 11 mm. long. Anteriorly it does not form part of the
margin of the anteorbital notch.
The lachrymal is irregularly oblong, with an external free margin 35 mm.
long and 12 mm. thick. The distance from the anteorbital notch to the
anterior end of the orbit is 60 mm. (Pl. 7, fig. 1.)
The lateral free margins of the basioccipital are extended posteriorly
beyond the exoccipitals, which is a character indicative of age.
The supraoccipital has a distinct median ridge, with a longitudinal
depression on each side, bounded externally by a prominent convexity.
(Pl. 10, fig. 1.)