In the Prochilodus, however, both these and the hones of the
lower jaw are feeble and are imbedded in the thick fleshy lips, to
which, and not to the bones themselves, the minute, flexible,
incurved, bristle-like teeth, characteristic of the genus, are attached :
they are arranged in a single close-set row.
The superior maxillary hones are edentulous, and are placed
backwards, transversely to the angle of the mouth in the subgenera
Schizodus, Serrasalmo, Myletes, and Xiphostoma; but in the true
Salmones and other cognate genera, they support a part, and often
nearly the whole of the teeth of the upper jaw.
In the Salmonidse of the River Nile, which belong to the genus
Citharina of Cuvier, the maxillary teeth are nearly as fine and as
close-set as in the Chsetodonts, but their free extremity is forked.
The pharyngeal hones are beset with velutine teeth.
In the Schizodus, the intermaxillary and premandihular teeth are
broad, and of the incisive type of form, with a crenate superior
margin. In the Serrasalmo, (PL 48, fig. 8,) the corresponding teeth
preserve the compressed form, but have a sharp apex, a broad base,
and trenchant and finely serrate edges ; these lancetted teeth are
arranged in a single series both above and below.
The Myletes is remarkable for the prismatic three-sided figure
of its teeth, the working surfaces of which are cuspidated by the
production of the angles into sharp points, (PL 48, fig. 10)V There
is a single series of these teeth in each premandihular, and a double
row in each large intermaxillary bone ; behind the two median teeth
of the lower jaw there are two simple conical pointed teeth ; similar
but much smaller pointed teeth are scattered over the pharyngeal bones.
In the genus Raphiodon(l) the teeth, as the generic name implies,
are long, slender, and extremely sharp-pointed ; they are implanted in
the short intermaxillary, the superior maxillary and the premandihular
bones; shorter teeth of a similar shape, alternate with the longer ones ;
the pair next the symphysis of the lower jaw, exceed all the rest in
size.
The elongated jaws of the species of Xiphostoma are provided
with a single row of small, sharp-pointed, slightlv-reflexed teeth ;
those on the alveolar border of the short superior maxillaries
(1) paipig, acus, aScvg, dens.
which cross obliquely the angle of the mouth, are directed forwards.
In the genus Saurus, the mouth presents the anomalous condition
among fishes of edentulous intermaxillaries, with a formidable array
of teeth in the upper jaw, supported exclusively by the superior
maxillary hones ; these meet at the middle line, and the small intermaxillaries,
which are recognizable by their characteristic ascending
process, are placed above and parallel to the median extremities of
the maxillary bones ; the teeth are slender, conical, and very acute ;
they are arranged in three or four rows, and form conical groups, with
the longest tooth in each placed innermost; these teeth have their
apices slightly expanded. Similar spear-shaped teeth are arranged on
the premandihular bones below; and likewise crowd the palate,
the tongue, the branchial arches, and the upper and lower pharyn-
geals.
The disposition and usual form of the teeth in the typical genus
Salmo are represented in a diminished view of them in the common
salmon, as seen in looking into the cavity of the open mouth, (Pl.
48, fig. 9). The teeth all present the same simple form, short,
stout, pointed, and incurved ; from four to five are implanted in each
intermaxillary bone, the remainder of the single row which arms the
upper margin of the mouth, being supported by the superior maxillary
bones. In the young salmon there are two or three teeth on each
side of the anterior part of the vomer | but, as growth proceeds, they
are reduced in number, and finally disappear in aged fish ; each
palatine hone supports a single row of teeth, nearly parallel with,
hut smaller than, those of the maxillary rows ; there is a single row,
on each premandihular bone ; and a double row united by a crescentshaped
series on the anterior part of the tongue. The pharyngeal
hones are armed with similar teeth.
The principal difference observable in the allocation of the teeth
in the species of Salmo obtains in the vomer; upon which, in the
salmon-trout and common trout(l) for example, the teeth are extended
backwards in a row, and deeply indent the surface of the tongue
between the two lateral rows of lingual teeth.
The teeth are anchylosed by their bases to the several dentigerous
(1) Mr. Yarrell has given a figure of the dentition of the common trout in vol. ii, p. 3, of
the British Fishes.