characters of great value in the determination of both recent and
extinct forms.
The teeth of the genus Lamna present an elongated triangular
sub-compressed form, with the anterior or outer surface less convex
than the posterior, especially in the median teeth and in those of the
lower jaw. The margins are trenchant and converge to a sharp
point, equally or symmetrically in the median teeth, but unequally
in the lateral ones in which the point is inclined backwards. In
some species, as in the porbeagle shark {Lamna Cornubica), and in
that great extinct species of which the teeth occur in the London
clay and other members of the eocene formation in this country, and
on which Agassiz has founded his sub-genus Otodus,{l) the teeth are
complicated by a small accessory cusp on each side of the base of
the principal cone. In other species, as in the Lamna oxyrhina of
Cuv. and Val., (PL 3, fig. 1 ,) the accessory cusps are wanting, at least
in large and full grown specimens : in both subgenera of Lamna, the
third vertical row of teeth counting backwards in the upper jaw is
much smaller than the contiguous rows(2) ; the rest gradually diminish
in size as they are situated nearer the angles of the mouth. In the
sub-genus Odontaspis, the teeth are narrower than in Lamna, the middle
cusp is longer, straighter, and more acute, and is provided with
two similar sharp pointed cusps on each side of its base. In the
upper jaw, the fourth, fifth, sixth, and seventh vertical rows of teeth
are smaller than the contiguous ones ; in both jaws, the first tooth is
small and the posterior teeth progressively diminish as they approach the
angles of the mouth. (3) The size and strength of the teeth thus modified
for piercing and lacerating render the Odontaspis the most formidable
among the shark tribe ; and the habits of the typical species,
(Odontaspis ferox) as indicated by its trivial name, correspond with
(]) PI. 5, fig. 5.
(2) M. Agassiz in his description of the dentition of this genus, mentions as one peculiarity
of it that, “ la troisième et quelquefois la quatrième et la cinquième dent de la mâchoire inférieure
est sensiblement plus petite que les autres, tandis qu’à la mâchoire supérieure les dents, à l’exception
de la première qui est plus petite que les suivantes, vont en diminuant uniformément
de grandeur jusqu’à la partie postérieure de la gueule.” In a skull of the Lamna Cornubica now
before me, I find, as in the Lamna oxyrhina, (PI. 3, fig. 1,) that the sudden diminution of size in
the third tooth is characteristic of the upper and not of the lower jaw.
(3) PI. 3, fig, 2.
■ the destructive character of its maxillary armour. The characteristic
■ dentition, of the shark tribe may be studied with advantage in the
■ spotted and spiny dog-fishes common on our coasts ; the former,
■ which is the type of the genus Scyllium, exhibits teeth of a triangular
«form with a large middle cusp, complicated, at least, in the young
■ animal, with one or two small cusps on each side of its base ; the
■ base is always more or less furrowed longitudinally. In CrossoThinus,
1 a sub-genus of Scyllium, the teeth are characterized by having the
■ osseous base divided into three lobes. In Ginglimostoma, the teeth have
I a simple rhomboidal base supporting one large median cone, and from
■ two to four obtuse denticles on each side : the teeth of this genus of
I dog-fish are remarkable for their somewhat unusual number, there
■ being frequently ten in each vertical row.
In the spiny or piked dog-fish fSpinax, Cuv.), the teeth (PI. 3,
■ fig. 3 ,) are alike in both upper and lower jaws; they are thin tnan-
■ gular plates with the apex inclined backwards, so that the anterior
I edges are opposed to each other ; the enamel does not terminate
I below in a horizontal line, but is continued along the middle of the
■ bony base. In an allied species, the teeth of the upper jaw are
1 smaller and of a different form from those of the lower jaw, being tri-
■ cuspid, as in the spotted dog-fish; some ichthyologists restrict the
I subgeneric name Spinax to the spiny dog-fishes which are cha-
■ racterized by this modification of the teeth.
In the genus Notidanus, the teeth are not only of different forms in
I the upper and lower jaws, but also vary considerably, in this respect,
■ at the anterior and posterior regions of the same jaw, (PL 3.)
I In the upper jaw, the anterior teeth are large, compressed, triangular
1 plates, with the pointed apex arched backwards, and the margins
1 slightly dentated, except in the two anterior ones. The posterior
I teeth are in the form of simple obtuse furrowed tubercles. In the
I lower jaw, the large anterior teeth have the apex less produced ; the
fl anterior margin is finely serrate, and the posterior I divided into three or more denticles. The posterior minute teeth resemble those in the
I upper jaw. Of the larger teeth there are rarely more than four in
I each vertical row.
In the subgenus Carcharias, the teeth present the form of