86 SILUROIDS.
In the genus Acanthicus,( 1) the maxillary teeth are bisinflected |
the first, or anterior tooth of each of the radiating rows, is the
shortest, and is curved outwards, the rest, to the number of seven
or eight, being bent backwards : there are from twenty-five to thirty
of these rows on each side of both upper and lower jaws.
The setaceous teeth of the Rhinelepis{2) have a similar arrangement
in antero-posterior radiated rows, and a similar moveable connection
with the maxillary membranes ; but the foremost tooth in each
row has its inflected summit split, and thus presents the singular form
of a bicuspid hook ; the posterior succeeding teeth, in each row, have
a simple hooked apex.
The foremost tooth of each radiated series in the Hypostoma{3)
is much shorter than the second, and is bent outwards : the second,
third and fourth teeth, counting backwards, are twice curved, with
the apex bent inwards ; the succeeding teeth grow shorter, present a
simple curve, and thus gradually disappear.
In the Loricaria the bisinflected setaceous teeth are arranged in a
simple series along the alveolar border of the intermaxillary and pre-
mandibular bones : the summit of each tooth is curved inwards and
backwards.
From the constancy observed in the different sizes, shapes and
directions of the teeth composing the vertical or radiated rows in
the above genera, it is to be inferred that they do not succeed each
other, and are not on the constant move from behind forwards,
as in the Plagiostomous fishes, with which in other respects the
teeth of the Goniodonts offer some striking analogies.
SILUROIDS.
33. The dental armature of this extensive and singular family of
fresh-water fishes is never of a predatory or formidable character,
the teeth being always small and simple, or of a minutely villiform
kind. Some species are almost edentulous, but there are others
which exhibit peculiar conditions of the teeth not elsewhere observable
in the vertebrate division of animals.
In the genus Cetopsis a single series of simple conical teeth 1
(1) PI. 48, fig. 3. , (21 lb. fig. 2. (3) lb. fig. 1.
SILUROIDS.
projects from the premandibular and vomerine bones, and one or
more rows of similar teeth from the intermaxillaries. The corresponding
teeth in the Doras are either minutely villiform, or are
replaced by equally minute uncalcified papillae, which permanently
represent the very earliest stage of dental development.
The slightly calcified papillae on the intermaxillary and premandibular
bones of the Hypophthalmus are so minute as to require
the aid of a pocket lens for their detection: but the branchial arches
support more conspicuous organs, which are clearly referable to
the dental system :(1 ) these are slender, elongated, pointed, whitish,
rigid, and fragile lamellae, attached in a close-set row to the concave
side of the arch, and with their points projecting towards the gullet.
Those of the first pair of branchial arches are most developed,
equalling the gills in length ; the rest gradually diminish as they approach
the pharynx.
In the Pimelodus villiform teeth are arranged in several rows upon
the intermaxillaries and premandibulars, and a few gramform teeth
upon the vomer (Pimel. Spun*). In the Pimelodus ctenodus, the first row
of jaw-teeth is composed of larger, rounded conical denticles, with an
obtuse apex. Other species of Pimelodus have teeth on the palatine
bones, but not on the vomer : and the species called by Cuvier Pimelodus
genidens offers the singular peculiarity of a patch of moveable
calcified denticles upon the inside of each cheek, or lateral membrane
closing the mouth.
In the genus Platystoma, the intermaxillary, premandibular and
-vomerine bones are beset with broad bands of strong villiform and
setiform teeth gradually increasing in length as they are placed deeper
in the mouth :(2) the pharyngeal arches are covered with similar, but
finer denticles.
In the Plotosi, the vomerine teeth are obtuse and rounded.
The premandibular teeth of the Synodontes present compressed
crowns terminated at one end by a recurved apex, and attached by
the opposite end or base to a flexible peduncle. (3)
(1) Agassiz. Spix, Pisces Brazilienses, p. 15.
(2) PI. l, fig. 1, exhibits the under surface of the right intermaxillary bone of a Siluroid
fish of the subgenus Platystoma,
(3) “ La mâchoire inférieure porte un paquet de dents très applaties latéralement, terminées