from the Shales of the Northumberland Coal-field. 365 
The remains in our possession of such fishes are divisible 
- into two species by the characters of the spines, scales, and 
teeth. One of these is very much larger than the other. It 
is the smaller of the two that appears to be identical with A. 
Wardi. 'The larger species is probably the same as that of 
which Sir P. Egerton had obtained the head and anterior 
oe and which is supposed by him to “ have measured two 
eet six inches in length” *. A pectoral spine of this is stated 
to have been three and a half inches long. 
The mandibular ramus of A. Wardi (Pl. XV. fig. 6) is 
about one inch and a half long and a quarter of an inch 
wide at the broadest part, which is near the proximal extre- 
mity, whence it tapers gradually to the distal end, which 
is rounded; the proximal end turns upwards, and presents a 
well-defined concave articular surface. The dentigerous bone 
is very thin, and its walls are usually pressed close together ; 
_the outer wall is irregularly striated longitudinally, the inner 
wall is smooth; the lower margin is strengthened by a stout 
styliform process, c, which is very liable to detach itself, when 
- it assumes the appearance of a cylindrical spine graduating to 
a point in front; it is united behind to the articular process, 
and is probably nothing more than a prolongation of the 
angular bone. 
his styliform process has been described as the entire 
mandibular ramus in some of the Acanthodet, and is seen oc- 
casionally attached to the head,—the dentigerous bone, with 
the teeth, having been detached. “In Sir P. Egerton’s figure 
of A. Wardi these styliform bones, so denuded, are seen still 
articulated to the head and thrown backwards. The teeth 
are frequently found attached to the thin-walled dentigerous 
bone, the styliform process having probably been left so at- 
tached to the head. 
_ The teeth are never found separated from the bone. There 
are five or six in each ramus, two of the larger being in the. 
centre, the smaller ones in front and behind; they are com- 
pressed in the direction of the jaw, and when seen in this po- 
sition they have the shape of as many equilateral triangles 
with the fatered margins a little hollowed towards the apices, 
which are recurved; they are expanded at the base, where 
oy become confluent, and are coarsely and irregularly stri- 
ated from one extremity to the other; and the surface being 
liable to erosion, the striation is frequently exaggerated. 
The upper jaw is coextensive with the mandible, and is ap- 
parently formed of one piece. The teeth are like those of the 
under jaw, and lock very accurately into them; they are of 
* Quart. Journ. Geol. Soc. vol. xxii. p. 470. 
