less constricted at their base, and supported on a short pedicle, which
is anchylosed to the osseous substance of the jaws.' (PI. 30, fig. 1).
The detached hemispherical teeth of the Lepidoid fishes are so like
those of some of the genera of the Pycnodont family, as to be scarcely
distinguishable.
The only difference which M. Agassiz recognizes between
the teeth of Lepidotus and those of Splicer odus is, that in the former
they have a slight constriction at the base of the enamel. But having
ascertained this character not to he constant, I submitted the teeth of
the Lepidotus Mantellii to microscopic examination, and have compared
their intimate texture with that of the similarly shaped teeth of Sphcero-
dus Bucklandi. The dense substance of the tooth of the Lepidotus (PI.
31) is composed of fasciculate tubes continued directly from the cells
of the osseous base, radiating, with a direction vertical to the surface
of the tooth, and giving off branches, at an acute angle, from their
very commencement; thus far the general character of the texture of
the tooth is the same as that of Sphcerodus, afterwards to be described;
hut the fine branches into which the fasciculate tubes resolve themselves
in Lepidotus, diverge at a much more open angle from the main
trunk, are spread out more widely, are more curved, and present
the appearance of the stems of corn beaten down with heavy rain.
These fine terminal branches are inextricably interwoven, and present
the appearance of numerous anastomoses, hut do not form so dense a
plexus of calcigerous tubes and cells as in the teeth of Sphcerodus in
which the corresponding tubes and cells intercept the light.
PYCNODONTS.(l)
28. In this family of fishes, of which all the representatives
are extinct, the teeth present a greater diversity of character, and
a higher degree of development than in the preceding; the prevalent
form approaches to that of the Lepidotus; the teeth being generally
adapted for crushing, and having a smooth convex or flattened crown.
In some genera they attain a very large size; when smaller they are
arranged in several rows. They have been observed in the intermaxillary,
premandibular, palatine and vomerine bones.
(X) irvicvog, thick, oSovg, a to o th ; thick-toothed fishes.
PYCNODONTS. 71
Tn the genus Pycnodus the teeth are more or less elongated, with
the crown slightly expanded, and convex and smooth above. The disposition
of these teeth on the vomerine bone is seen in figs. 1 and 2 ,
PL 34. A central row of transversely oval grinders is bounded on each
side by a double alternate row of smaller circular teeth. Similarly
shaped teeth were arranged in three or four rows on the jaws ; but the
exact number and disposition of the maxillary teeth have not yet
been ascertained.
The modifications of external form which characterize the teeth
of the different species of this genus, which have yet been discovered,
are exhibited in the great work on Fossil Fishes by M. Agassiz,
tab. 7S2p,h cde,r vodoul.s .i—i. This genus is founded on detached teeth, which are
the sole remains of the species composing it that have as yet been
brought to light. These teeth are of a hemispherical form, with a
smooth upper surface, (PI. 3 3 , figs. 1 and 2), and most probably were
distributed over the same bones as in the Pycnodus. The basis of the
tooth is a bone of the coarse cellular structure usual in osseous Fishes.
(PI. 32). The body of the tooth consists of coarse tubes, which arise insensibly
from the basis, where they have a diameter of vAnr th of an inch,
and proceed directly and perpendicularly to the surface of the tooth.
The characteristics of these tubes are, first, that they are so closely arranged
together that only one-fourth of their own diameter intervenes
between them at their origins. Secondly, they present the appearance
of being composed of a closely-twisted bundle of smaller tubes,— an
appearance produced by the oblique direction and acute angle at
which the calcigerous tubes are continued from them into the clear
intervening substance. Besides these smaller tubes, the mam trunks
begin immediately to give off short and somewhat coarse branches at
very acute angles ; these branches increase in number, and the trunks
proportionally diminish,- until they have traversed two-thirds of the
vertical diameter of the tooth ; they then resolve themselves into fasciculi
of extremely minute twigs, which interlace together, and in many
places dilate into, or communicate with, numerous minute calcigerous
cells, and form so dense a layer as to intercept the light, excepting