triangular plates with a broad base, sharp apex, and trenchant or I
finely dentated edges. The anterior surface is nearly flat, the poste- I
rior slightly convex i the teeth of the lower jaw are rather narrower, I
and thicker, and somewhat smaller than those of the upper jaw. I
The dentition figured(l) is that of the great and formidable “ white I
shark” of navigators,—the type of the subgenus Carcharodon of I
Müller. In the United Service Museum there are preserved the I
jaws of a Carcharodon, of which the upper one measures four feet and I
the lower one three feet eight inches, following the curvature. The I
length of the largest tooth is two inches, the breadth of its base one
inch nine lines : the total length of the shark was thirty-seven feet.
Fossil teeth precisely corresponding in form with those of the Carcharodon
occur abundantly in the tertiary formations of both the old and I
new continents ; some of these teeth exhibit the extraordinary dimensions
of six inches in length, and five inches across the base. If, therefore,
the proportions of these extinct Carcharodons corresponded with
those of the existing species, they must have equalled the great
mammiferous whales in size ; and, combining with the organization of
the shark its bold and insatiable character, they must have constituted
the most terrific and irresistible of the predaceous monsters of
the ancient deep.
In the blue-shark, ('Carcharias glaucus, Cuv.), the teeth of the
lower jaw are longer and narrower than in the white-shark, and approach
nearer to the form characteristic of the genus Lamna; they
may be distinguished, however, by their broader base, the angles of
which are less produced downwards, and by their finely dentated edges.
In the subgenus Physodon, which is nearly allied to Carcharias, the
teeth of one or two median rows are disproportionately small.
The teeth of the hammer-headed sharks (ZyganaJ, are triangular
flattened plates, with finely dentated margins, as in Carcharias, but
the points are bent backwards, and the posterior margin is concave. (2)
In the genus Galeus, to which the grey-shark or tope of our coast
belongs, the teeth are relatively thicker than in the Zygccna, and the
posterior margin is notched, with the basal part produced backward,
and divided into three or more denticles : the anterior margin is
(1) PI, A, fig. 1. , (2) PI. 4, fig, 2.
finely serrated. (1), This description applies to the lateral rows of teeth
in which the points are inclined backwards and outwards; the teeth
of the mesial row in both jaws are of a symmetrical figure. The
teeth are alike in the upper and lower jaws.
There is the same correspondence, as regards the upper and
lower jaws in the singularly formed teeth, which characterize the
Squalus spinosus of Schneider,—the type of the genus Goniadus of
Agassiz (PI. 4, fig. 4). In these teeth, the point is so far inclined
backwards, that the anterior margin forms a nearly horizontal
trenchant edge, applied to the corresponding margin of the opposite
tooth: two denticles project horizontally forwards from the base of
the anterior margin, and one or two similar denticles from the opposite
side of the tooth.
In the genus Scymnus, (PI. 4, fig. 3,) the teeth of the lower differ so
much from those of the upper jaw, that nothing save actual inspection
of the jaws in situ could lead to the belief that they belonged
to the same animal. The teeth of the upper jaw are small,
conical, subcompressed, with slightly recurved points ; those of the
median or anterior rows present a nearly subulate form: the posterior
ones are somewhat broader : their osseous base is bifurcate, as in
Lamna. The teeth of the lower jaw are about eight times larger than
those above; they are straight, flattened, symmetrical, lancet-shaped
plates, with finely dentated margins. The base of the tooth is bifurcate,
the divisions being parallel, and divided by a fissure which becomes
slightly dilated near the enamelled crown. The middle tooth of the series
rests upon the symphyseal line, and has one basal fork attached to
each ramus of the lower jaw ; its parallel lateral edges overlap those
of the contiguous teeth; the posterior edge of each lateral tooth
overlaps in a similar manner the anterior one of the tooth behind:
this imbricated disposition is quite peculiar to the Scymnus, among
sharks. There are four recumbent teeth in each vertical row, the
apices of which are turned down in a direction diametrically opposite
to that of the erect exterior tooth. The shedding of the outer teeth
appears to be simultaneous, and the change of position of the succeeding
series must be very rapid, as well as extensive.
(1) PI. 28, fig. 9.