The teeth are of the most formidable description, consisting
in both jaws of serrated dental plates behind, and in front of
enormous conical tusks (fig. 102, a). Though immensely larger,
the teeth of _Dinichthys_ present a curious resemblance to those
of the existing Mud-fishes (_Lepidosiren_).
In another great group of Devonian Ganoids, we meet with fishes
more or less closely allied to the living _Polypteri_ (fig. 105)
of the Nile and Senegal. In this group (fig. 106) the pectoral
fins consist of a central scaly lobe carrying the fin-rays on
both sides, the scales being sometimes rounded and overlapping
(fig. 106), or more commonly rhomboidal and placed edge to edge
(fig. 105, A). Numerous forms of these "Fringe-finned" Ganoids
occur in the Devonian strata, such as _Holoptychius, Glyotoloemus,
Osteolepis, Phaneropleuron_, &c. To this group is also to be
ascribed the huge _Onychodus_ (fig. 102, d and e), with its
large, rounded, overlapping scales, an inch in diameter, and its
powerful pointed teeth. It is to be remembered, however, that
some of these "Fringe-finned" Ganoids are probably referable
to the small but singular group of the "Mud-fishes" (_Dipnoi_),
represented at the present day by the singular _Lepidosiren_
of South America and Africa, and the _Ceratodus_ of the rivers
of Queensland.
[Illustration: Fig.
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