590 



FISHES OF THE OLD RED SANDSTONE, 



tions are in fact less distant from each other, than they are from the round part of the snout. The 

 middle of the head, including the region of the eyes, the cranium and the occipital crest, is 

 elevated, whilst the sides and anterior edge are considerably dilated and horizontally extended, so 

 that the two horned prolongations of the head overlap the sides of the body and extend considerably 

 behind it, as seen in PL 1. f. 1. It is probable the head only appears to extend so much below the 

 body, because the left wing of the disk has been bent back into a more vertical position than was 

 natural to it. The eyes are placed in the middle of the shield, and near each other, but a little 

 nearer to the end of the snout than the occipital crest. They appear to have been directed straight 

 upwards, as in the Uranoscopes ; at least such is their position in the specimens best preserved, 

 and which are completely extended in their natural state, PL 2. f. I. In PL 2. f. 2. where the 

 sides appear to be somewhat contracted, the eyes are a little inclined towards the sides. Between 

 them and in front of the orbits there is a triangular depression, which appears to have been occupied 

 by the nostrils. Behind the orbit is another longitudinal narrow depression, bordered by two 

 projecting crests, probably the parietofrontal crests, so that the depressions would be found at 

 the junctions of the frontal bones. These crests approach each other behind, and rise to form the 

 occipital crest, which is very prominent, as is seen in PL 2. f. 2, whilst in f. 1. they are almost 

 broken away. The posterior and middle portion of the head is nearly square, and is edged by the 

 first series of scales, whilst the sides are very much sloped, and form the interior border of the 

 lateral prolongations of the disk of the head, PL 2. f. 2. and PL 1. f. 2. 



"The outline of the disk is surrounded by a bony plate, which, being bent back on itself, forms 

 the inferior, as well as lateral margin of the head. Unable to determine the form and connection 

 of the bones of the cranium, in consequence of the state of preservation of the head, (probably the 

 result of its structure,) I proceed to notice the appearance of other parts of the surface of the head. 

 The exterior surface is in a great measure covered by irregular scales, in form approaching to 

 circular, the edges of which, notwithstanding they are more or less straight, are united in juxta- 

 position, so as to form a pavement of scales, exactly similar to those which cover the heads of the 

 Ostracions. Each of these scales has a convex centre, and hollow furrows diverging towards the 

 edge, where they form a denticulation by which one scale is dove-tailed into another. The form 

 of these scales varies extremely ; the greater part are circular, but some are angular ; the latter are 

 attached to the straight edge of a scale, which on other sides is circular, and here and there small 

 ones are seen filling up the intervals between the larger. These scales are bony, and their exterior 

 surface enamelled. At the outline of the disk they are more confused, and the furrows of the 

 enamel are parallel to the edge. (See a profusion of these scales in PL 2. f. 1. and magnified repre- 

 sentations of them in PL 1. f. 7«) 



u The bones of the head have also a fibrous structure, as may be seen in all the specimens 

 where any fragments of it remain. This fibrous structure is most clearly observable on the internal 

 surface of the disk as represented in PL 1. f. 1.; also PL 2. f. 1. in the place where the scales are 

 removed ; and even on the specimens which are merely casts, where it may be traced in relief upon 

 the rock, on which the sinuosities of the interior surface of the bones of the head are left as im- 

 pressions. On the anterior part of the disk the osseous fibres are directed straight forward ; on 

 the sides they are oblique, afterwards transverse ; and lastly, in the lateral prolongations of the 

 crescents of the head, they follow the direction of these prominent parts, and appear in general to 

 diverge to every point from the sides of the cranium. The bones of the cranium itself, present a 

 similar radiation between the parietofrontal crests, as seen in PL 2. f. 1. The lateral prolongations 

 of the head are thicker than its bony membranes, and narrow insensibly, so as to form a round and 



