ram of the jaws and teeth of _Dinichthys Hertzeri_,
viewed from the front, and greatly reduced; b, Diagram of the
skull of _Macropetalichthys Sullivanti_, reduced in size; c,
A portion of the enamelled surface of the skull of the same,
magnified; d, One of the scales of _Onychodus sigmoides_, of
the natural size; e, One of the front teeth of the lower jaw of
the same, of the natural size: f, Fin-spine of _Machoeracanthus
major_, a shark-like fish, reduced in size. (After Newberry.)]

[Illustration: Fig. 103.--_Cephalaspis Lyellii_. Old Red Sandstone,
Scotland. (After Page.)]

[Illustration: Fig. 104.--_Pterichthys cornutus_. Old Red Sandstone,
Scotland. (After Agassiz.)]

The Devonian Galloids belong to a number of groups; and it is
only possible to notice a few of the most important forms here.
The modern group of the Sturgeons is represented, more or less
remotely, by a few Devonian fishes--such as _Asterosteus_; and
the great _Macropetalichthys_ of the Corniferous limestone of
North America is believed by Newberry to belong to this group. In
this fish (fig. 102, b) the skull was of large size, its outer
surface being covered with a tuberculated enamel; and, as in the
existing Sturgeons, the mouth seems to have been wholly destitute
of teeth. Somewhat allied, also, to the Sturgeons, is a singular
group of armoured fishes, which is highly characteristic of the
Devonian of Britain and Europe, and less so of that of America.
In these curious forms the head and front extremity of the body
were protected by a buckler composed of large enamelled plates,
more or less firmly united to one another; whilst the hinder end
of the body was naked, or was protected with small scales. Some
forms of this group--such as _Pteraspis_ and _Coccosteus_--date
from the Upper Silurian; but they attain their maximum in the
Devonian, and none of them are known to pass upwards into the
overlying Carboniferous rocks. Amongst the most characteristic
forms of this group may be mentioned _Cephalaspis_ (fig. 103) and
_Pterichthys_ (fig. 104). In the former of these the head-shield is
of a crescentic shape, having its hinder angles produced backwards
into long "horns," giving it the shape of a "saddler's knife."
No teeth have been discovered; but the body was covered with
small ganoid scales, and there was an unsymmetrical tail-fin.
In _Pterichthys_--which, like the preceding, was first brought
to light by the labours of Hugh Miller--the whole of