220 Dr Hiszert on the Limestone of Burdiehouse, 
There is a small proportion of soda in the recent bones, and perhaps a less pro- 
portion of potash and soda existing partly as chlorides in the Gyracanthus. 
The proportion of animal matter in the bones of the pike amounts to as much as 
$7.36 parts in a hundred, of which a trace only appears in the Gyracanthus for- 
mosus. 
Having stated these differences, I shall first make some. remarks on the great 
quantity of phosphate of lime possessed by the fossil ray. 
Mr Conn 1 has very properly remarked to me, in reference to the Gyracanthus 
having been assigned to the family ofthe Cestraciontes, that the Cestracion is consi- 
dered as a cartilaginous fish, whilst the great quantity of bone-earth contained in 
the dorsal ray of the fossil animal, amounting to 54 per cent., is incompatible with 
the notion of its being any thing but bone. Now, I certainly find it remarked of 
cartilaginous fish, that, while the skeleton of these animals remains constantly carti- 
laginous, in rare cases only it contains osseous fibres; the calcareous matter being 
in such instances deposited simply in the form of small grains. There are, at the 
same time, certain fish of this class, though appearing to separate themselves from 
it, as, for instance, the orders of Chismopnea and Teleobranchia, among which the 
skeleton is fibrous, and becomes with age perfectly osseous. 
To such a structure, therefore, I would refer the fossil dorsal rays of the Gyra- 
canthus, which appear to have been formed of osseous fibres, disposed in a longitudi- 
nal manner (as can even be traced in their mineralized structure), the intervals or 
pores having been originally filled with animal matter. This arrangement of. struc- 
ture is.indeed remarkably shewn in some fossil specimens, where elongated pores, or 
tubes, larger than common, are filled with siliceous matter. 
Another remark is suggested by the mode in which the loss of animal matter has 
been supplied in the fossil rays of the Gyracanthus. It would here seem, that the 
bones of the pike contain, in addition to the phosphate of lime, about six parts in a 
hundred of the carbonate of lime. Now, it is remarkable that the fossil thorny ray 
contains as much as $4 parts nearly of the carbonate of lime, along with only 10 
parts of siliceous matter, by which it appears that the loss of animal matter has been 
very readily supplied by infiltrations of calcareous matter, derived no doubt from a 
calcareous matrix, but comparatively little with siliceous matter. Ought this cireum- 
stance to throw any light upon the original organization of these rays ? 
There is, at least with myself, much difficulty in explaining why the loss of animal 
matter is chiefly supplied in these fossil rays by carbonate of: lime, which is exactly 
the reverse of what appears to have taken place in fossil scales. Whether, in this 
instance, the animal matter has been sooner released from the substance of the bone, 
and, as a consequence, its place more directly supplied by infiltrations of calcareous 
matter from the matrix of these relics. I will not pretend to determine. In the dense 
and compact structure of the bony scales of the Megalichthys, the mineralization 
might have gone on far more slowly ; and hence the substitution of a great excess of 
siliceous matter. 
