the head
and the front part of the body were defended by a buckler of
firmly-united enamelled plates, whilst the rest of the body was
covered with small scales. The form of the "pectoral fins" was
quite unique--these having the shape of two long, curved spines,
somewhat like wings, covered by finely-tuberculated ganoid plates.
All the preceding forms of this group are of small size; but
few fishes, living or extinct, could rival the proportions of
the great _Dinichthys_, referred to this family by Newberry.
In this huge fish (fig. 102, a) the head alone is over three
feet in length, and the body is supposed to have been twenty-five
or thirty feet long. The head was protected by a massive cuirass
of bony plates firmly articulated together, but the hinder end
of the body seems to have been simply enveloped in a leathery
skin. 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. 105.--A, _Polypterus_, a recent Ganoid
fish; B, _Osteolepis_, a Devonian Ganoid; a a, Pectoral fins,
showing the fin-rays arranged round a central lobe.]

[Illusration: Fig. 106.--_Holoptychius nobilissimus_, restored.
Old Red Sandstone, Scotland. A, Scale of the same.]

Leavi