situated on the outer part of this expanded extremity of the vomer in
the present species of Labyrinthodon. The corresponding part of the
vomer in the Menopome and gigantic Salamander supports a transverse
row of small teeth; and the large tooth of the Labyrinthodon
is the outermost of a similar transverse row of teeth extending, five in
number, across the anterior expansion of each lateral moiety of the
vomer, the three median teeth being small and equal, the two outermost
much larger. In the present fossil these teeth appear to have
been alternately shed ; that is the first, third, and fifth, counting-
outwards from the middle line are in place; the second and fourth
are indicated by their empty sockets. This is analogous to the
condition of the maxillary series of teeth ; it is a course or order
of shedding and renewal which is common in many fishes, where
these processes succeed each other frequently and quickly, and by
which the dental series is always kept in an efficient state. The
outermost or fifth tooth is placed behind, as well as to the outer side
of the socket of the fourth displaced tooth ; and while it terminates
the transverse row of the vomerine teeth, it forms the commencement
of a longitudinal row of small and equal-sized teeth which is continued
backward along the outer margin of each vomerine bone (fig. 3 c);
the whole of the vomerine series of teeth thus describes a curve,
nearly concentric and parallel with the external maxillary series of
teeth ; and the large fangs occupy corresponding situations in both
the outer and the inner row of the teeth of the upper jaw.
In the Saurian reptiles, the examples of such an inner or
palatal row of teeth are comparatively few, and the series, when
it does exist, is very short, and is situated towards the hack of
the palate upon the pterygoid bones, as in the iguana, aporo-
mera and mosasaur. In the Ophidians, the inner rows of teeth
are situated on the palatine and pterygoid bones, and are never
arranged transversely to the axis of the mouth. In the Ba-
trachians this is the most common disposition of the palatal
teeth; they form a short transverse series at the posterior
part of the divided vomer in the frog, and at the anterior part
of the vomer in the menopome and gigantic salamander; in the
amphiume, the palatal teeth form a nearly longitudinal series, along
each outer margin of the long and narrow vomer ; the extinct Labyrinthodon
combines both these dispositions of the vomerine teeth.
The next fossil which I proceed to describe, and which, like the
preceding one, is from the sandstone in the neighbourhood of
Warwick, also throws much light upon the dental system and
affinities of the present singular genus of extinct reptiles. It is the
anterior dentigerous part of the ramus of the lower jaw, a portion
of which is figured at PL 63 a , fig. 2. This ramus is slender,
straight, and with its symphysial extremity abruptly bent inwards,
the inner line of the symphysis here forming a regular and deep
curve. The breadth of the bone at the posterior fractured part
is ten lines; at the anterior part, behind the inflected symphysis,
seven lines; the breadth of the anterior fractured portion is one
inch. The structure of this long and straight ramus of the jaw
presents almost as striking a batrachian character as any of those
derived from the foregoing fossil; that is to say, the angular piece
is of great breadth, and is continued forwards to near the symphysis,
forming the whole of the inferior part of the ramus of the
jaw extending upon the inner as far as upon the outer side of the
ramus ; the inner plate performing the function of the detached
“ os operculare ” in the lower jaw of the Saurians. The dentary
piece is supported upon a deep and wide groove, extending along the
upper surface of the angular piece and looking obliquely outwards.
The angular piece projects beyond the outer edge of the groove,
so as to form a strong convex ridge on the external side of the jaw
below the dentary piece • this character, which in the large hull-frog
(Rana pipiens) is confined to the posterior part of the maxillary
ramus is here continued to near the anterior extremity, and forms a
conspicuous character of the jaw of the Labyrinthodon. The teeth
in the present ramus are long and slender, and so closely correspond
in size and shape with those in the upper jaw, just described, that
they must be regarded as belonging to the same species.(1) There are
not less than fifty sockets in a single linear series, and at the anterior
inflected part of the jaw there is the base of the socket of a large
tooth, six lines in diameter: the serial teeth gradually diminish in
(1) The specific name, leptognathus, relates to the slenderness of this long lower jaw.
P 2