each premandibular bone were opposed to the molar teeth above.
The side view of these teeth (PI. 30, fig. 4) shows their elevation above
the jaw. In the vomer, a median row of transversely oblong teeth is
bounded by smaller subcircular teeth, as in the other Pycnodonts.
SAUROIDS.
29. This family of voracious fishes is represented in the existing
creation by extremely few species, which are severally the types of the
genera Lepidosteus, Amia, and Polypterus; and these genera are distributed
at remote distances in the great rivers of the American and
African continents. The general character of the teeth in this family
is to have larger ones of a conical form intermixed with more numerous
teeth of smaller size.
The Sauroid fishes have teeth on the intermaxillary, premandibular,
palatine and vomerine bones. These teeth are conical and
sharp-pointed: some are large, and are separated by interspaces
occupied by similarly shaped but much smaller and more numerous
teeth. The larger teeth are grooved longitudinally at the base, and
have a large conical pulp-cavity within. Their fluted base sinks into
an alveolar cavity of the jaw, but is intimately blended with its bonv
walls, in a manner which will be more particularly described in the
teeth of the Rhizodus.
In the jaws of the Polypterus of the Nile, there are two rows of
equal, fine, sharp, approximated teeth ; those of the anterior row are
the largest] the posterior ones are like the teeth of a rasp.
In the Stony-gar (Lepidosteus) of the North American rivers,
the elongated jaws are also armed with similar laniary and rasp-like
teeth: the outer row consists of numerous conical sharp-pointed
teeth, which are separated by regular intervals containing the sockets
of old teeth which have been shed, and the germs of new ones.
■ External to these larger teeth there is a less interrupted row of
smaller conical teeth. (1) The inner border of the dentigerous margin of
the jaw is beset with a series of small rasp-like teeth; and similar
teeth are present on the vomer and the palatine bones. The larger
conical teeth are developed in alveolar cavities, but their basis becomes
(1) PI. 35, fig. 1.
anchylosed to the jaw-bone when their growth is completed; and, as
in most other fishes, the succession of new teeth seems to be uninterrUPt<
The extinct genera of this family were much more formidably
armed, and the great conical laniary teeth of some of the individuals
compete in size and strength with those of the largest Ichthyosaurs
and Crocodiles. Plate 35, fig. 2, is a reduced figure of the dislocated
and fractured premandibular bones of an extinct sauroid
species of the genus Rhizodus, a genus nearly allied to the Holop-
tychus of Agassiz, but differing in the greater number, and more
robust and obtuse shape of the smaller conical teeth. In each premandibular
bone there are three elongated conical teeth, with several
smaller and more obtuse conical teeth in the interspaces.
The larger teeth have an ovate transverse section, with a trenchant
posterior margin, and terminate above in a sharp point f they are
thus alike fitted for piercing and cutting. Their base is irregularly
fluted in the longitudinal direction, and sinks deep into the substance
of the jaw, with which it is firmly anchylosed. The peculiarly
efficient mode in which these large destructive teeth are implanted
in the jaws, indicates the violence and force with which they were
wielded in the predatory contests of the living fish. Fig. 1,P1. 36,
shows the external form of one of the larger teeth of the Rhizodus.
A longitudinal and vertical section has been removed from the
grooved base, showing its solidity, and the coarse longitudinal fibrous
structure which it presents to the naked eye. Fig. 2 exhibits the
complicated organization which a section of a portion of the basis of
the tooth presents under a magnifying power of | inch focus.
The exserted body of the tooth is hollow, as in other Sauroids,
but the pulp-cavity is relatively smaller g the parietes of this cavity
consist of a dense ivory, composed of minute calcigerous tubes. The
diameter of these tubes at their origin is -*Mh of a line. They proceed
in slight curvatures from the central canal at right angles to the
periphery of the tooth, with interspaces equal to four of their diameters ;
throughout their course they are minutely undulated, and occasionally
divide dichotomously ; they give off ramuscules at very acute angles,
which are lost in the clear interspaces. The thin external enamel