592 



FISHES OF THE OLD RED SANDSTONE. 



edge supports a large ridge of imbricated rays,, very thick in proportion to the size of this fish, 

 which enlarge from the posterior edge of the second dorsal to the middle of the pedicle, and which 

 diminish again insensibly to its extremity. These little rays are very thick in proportion to their 

 length. They are less strongly attached to the edge of the pedicle, and less inclined towards its 

 extremity than most of the other genera of this family* 



" The scales of the body are of a very peculiar form, and quite unlike those of any other genera. 

 Fishes of the genus Callichthys only have also on their sides a series of very elevated scaJy plates ; 

 but in the genus Cephalaspis, there is on each side only one range of plates, high and narrow, in- 

 serted transversely on the middle of the sides ; whilst on the edge of the back and the belly there 

 are series of little scales disposed obliquely to the extremities of those on the sides. On the pedicle 

 of the tail, and on its prolongation, the scales have all the same form, they are rhomboidal, and dimi- 

 nish in size. Those on the centre of the sides PI. 1 . f. 4, are so high that their breadth exceeds 

 their length eight or ten times, and they occupy more than half the height of the fish, at least in 

 its anterior division. Towards the middle of the body they are less high, and below the second 

 dorsal they end by being confounded with the little scales of the back and belly • so that the sides 

 of the tail and its prolongation do not present the striking disproportion which there is in front, 

 between the scales of the sides and those of the back and belly. The posterior edge of these high 

 plates is straight, perpendicular to the longitudinal diameter of the fish, whilst the superior edge is 

 cut off in a slope ; the posterior angle is much more elevated than the anterior one. At the 

 inferior edge, which is parallel to the superior, the obliquity of the angle is inverted. The exterior 

 surface of these scales is ornamented with undulated furrows disposed in the direction of their 

 greatest diameter. There are from 26 to 30 of these plates on the sides. The series of scales on 

 the edge of the back are placed obliquely at the extremity of the high scales of the side, and run 

 from top to bottom, from the front to the back, so that the opening of the obtuse angle which they 

 form together is turned towards the head, and its summit towards the tail. In PI. 1. f. 2. the dis- 

 position of this series is seen from the top, and their junction with the side plates ; each one is 

 composed of several scales as long on the anterior part of the back, as the ridges of the sides are 

 wide, but which become smaller in proportion as the latter diminish in height, and are soon con- 

 founded with the scales on the edge. Tn each of these series there appears to be from four to five 

 scales (f. 5.) : on the edge of the belly the scales are turned obliquely backwards, to the extremity 

 of the great transversa] plates. This series in (f. 3.) are much narrower than that of the back, and 

 appear to be formed of two scales only. Near the middle of the second dorsal all the scales are 

 about the same size ; those of the sides only are a little higher than they are long ; but towards 

 the extremity of the tail, they become more and more equilateral, and finish on the prolongation of 

 the pedicle in a lozenge- shape, (f. 6.) of which the sharp angles are in the longitudinal direction of 

 the fish. All these small scales appear smooth. 



" The analogy in the structure of the scales of the genera Callichthys and Cephalaspis, appears to 

 me to confirm the position I have assigned to the Go?ioidonts and Siluroids, in the order 

 Ganoids following the Accipensers or Sturgeons." 



2. Cephalaspis rostratus, Agass. (PL 2, f. 4 and 5.) Recherches, vol. ii. t. lb. {.6 and 7. 



" This species evidently belongs to the genus Cephalaspis as characterized in the preceding de- 

 scription, and differs essentially only in the form of the head, which is narrow and much elongated. 

 I have as yet only seen one good specimen, which is represented with its superior surface, fig. 6, 



