It is probable that the teeth in the Nantucket specimen, though quite large, did not project beyond the gums any considerable distance. The external border of the alveolar groove behind the tooth is only 20 mm. below the apex of the tooth, and it is not unlikely that the gums in a specimen of this size had nearly that thickness, so that only the tip of the tooth would project beyond them. Though the apex is acute, it has a flat abraded surface anteriorly, which, however, is but 4 mm. long. It seems probable, on the whole, that the teeth in the female may be quite large without projecting more than a few millimeters beyond the gums.

In shape the tooth of the Nantucket specimen is almost identical with that of Sowerby’s Brodie House adult male, as figured by Lankester. The dentine at the apex is more nearly white than the cement which surrounds it. The superior margin of the latter is not a plain ring, but sends upward a papilliform projection on each side. The dentine itself has two vertical grooves on each side. The root of the tooth ends very obliquely and is rugose and irregular. The cavity is closed.

Grieg remarks as follows regarding the structure of the teeth of the Rugsund specimen:

Sections and microscopic preparations of the alveolar tooth of this whale show that its apex consists of dentine, within which is found an inner pulp cavity 4 mm. long and 1 mm. broad. The dentine, the structure of which agrees with that which Turner found in Mesoplodon bidens and Mesoplodon layardi, is yellowish white, with the exception of the part nearest the pulp cavity, which is yellowish brown. It seems to correspond most closely to what Ray Lankester called osteodentine. Throughout the tooth the dentine is covered with a very thin layer of shining white enamel. The enamel is, however, lacking on the front of the tooth, having probably been worn away. A section through the middle of the tooth, at right angles with the V-shaped furrow, shows a yellowish cement layer from 3 to 5 mm. broad, which is, however, worn away on the front of the tooth. Within the cement layer is a white, amorphous, calcareous mass, forming a band from 1.5 to 3.5 mm. broad, which appears to correspond to Ray Lankester’s “globular matter” and Turner’s “modified vasodentine.” The mass seems to agree most closely with Ray Lankester’s “globular matter,” as it has “no structure excepting an indistinct botryoidal character visible with a low magnifying power.” The core of the tooth consists of dentine, the inner layer of which is brownish, while the outer is rather whitish yellow. As above mentioned, the dentine is visible on the front of the tooth, since both the cement and the amorphous, calcareous mass are worn away. Moreover, it is clear that on the front of the tooth the dentine is not covered by enamel. The pulp cavity is reduced to a fine pore. A section across the root of the tooth shows an outer yellowish cement layer, from 2 to 5 mm. broad, while the interior of the tooth is filled with a white, amorphous, calcareous mass, which is interspersed with thin yellowish lamellæ of dentine. Here and there, also, thin lamellæ are seen to extend from the outer cement layer into the white, amorphous, calcareous mass. The dentine lamellæ appear to be identical with what Ray Lankester calls osteodentine. No pulp cavity is visible in the root of the tooth.[15]

The dimensions of the Nantucket skull are given in the following table in comparison with those of seven European skulls of M. bidens. Dimensions of the Annisquam, Massachusetts, skull are also added for purposes of comparison, although it represents another species (see [p. 9]).

Dimensions of eight skulls of Mesoplodon bidens and one skull of M. densirostris (?).

Column headings: M. bidens. B: Nantucket, Massachusetts, 1867, M.C.Z., female? adult.a C: Scotland, 1872, Turner, female young.? D: Fæø, Norway, 1895, Grieg, female? young. E: Shetland, 1881, Turner, male adult. F: Rugsund, Norway, 1901, Grieg, male adult. G: Udsire, Norway, 1869, Malm, male (No. 1). H: Vanholmen, Sweden, 1881, Malm, male (No. 2). I: Landenæs, Norway, 1895, Grieg, male. M. densirostris. (?) J: Annisquam, Massachusetts, 1898, True, female young.

Measurements.BCDEFGHIJ
mm.mm.mm.mm.mm.mm.mm.mm.mm.
Total lengthb765+749620743±...733740660c622
Length of rostrumb483+489400......485500410c377
Tip of beak to end of pterygoidbd607+572.........582590517cd466
Height from vertex to pterygoid277241...254267272258235248
Breadth between orbitse277286f254267292293253f260[278]
Breadth between zygomatic processes289292262292295298270268266
Breadth at maxillary notches184197170184193187170175[166]
Breadth of beak at middle425138......3646g4038
Depth of beak at middle35...h31............h3351
Greatest breadth of premaxillæ proximally131127115114116129124122...
Greatest breadth of premaxillæ in front of anterior nares107102h104102108108100h7692
Greatest breadth of anterior nares54...53...5350505039
Length of temporal fossæ90...............h6682
Breadth between temporal fossæ222.....................208
Breadth of foramen magnum50.........4956548046
Length of mandiblec651ij470543i464...639640560...
Length of symphysis237241162......212220160...
Greatest depth of mandible106114921021161109795...

a The size of the teeth makes it quite certain that it is an adult female. b End of beak broken off about 30 mm. from tip. c Right side. Add 31 mm. for breakage. d In median line. e At middle. f Between “suprafrontal processes of max.” g Grieg’s fig., p. 18, shows 44 mm. h From Grieg’s fig., p. 18. i “Length of ramus.” Length of mandible=699 mm. j In Trans. Roy. Soc. Edinburgh, vol. 26, 1872, p. 776.

MESOPLODON DENSIROSTRIS (Blainville)?