from the Shales of the Northumberland Coal-field. _ 369 
ference, is only seven inches long, including the portion buried 
beneath the skin. : : 
_ All this seems to demonstrate, beyond doubt, that these are 
really paired spines, most probably pectoral; and from this 
wearing we may fairly assume that Gyracanthus was a ground- 
fish, and that the spines assisted its motions at the bottom of 
the water. 
The straight spines, or those which are not laterally bent, 
are all regularly arched from before backwards; and their 
distal or pointed extremities are all perfect, not being in the 
least degree worn. These are apparently dorsal spines; and 
that there is only one of such in each fish seems probable from 
the fact that they occur in the ratio of one to two of the paired 
spines, as shown by our previous division of the seventy-one 
specimens. 
The dorsal spines are considerably smaller than the paired 
ones; they are more compressed, and the posterior denticu- 
lated keel is more strongly developed; the extreme point is 
smooth, compressed, and rounded in front. The largest are 
about eleven inches long, and three and one-quarter inches in 
circumference at the thickest part. The paired spines are 
fifteen or sixteen inches in length, and upwards of six and a 
half inches in circumference. ; 
One or two specimens of the species denominated G. for- 
mosus have likewise occurred; and as the same spine of @. 
tuberculatus is occasionally found with both tuberculated and 
smooth ridges, the former can scarcely be considered a good 
species. M. Agassiz’s figure of G. formodsus*, like G. tuber-. 
culatus, is laterally bent. 
Large flat triangular bones are frequently found associated 
with the spines, measuring sometimes eight and a half inches 
long and six and a half inches broad at the widest part. 
Their structure is very open; and as they are seldom well pre- 
served, they are probably only imperfectly ossified; the bone- 
fibre radiates from the apex to the expanded base. There can 
be little doubt that these are carpal bones, similar to those in 
connexion with the pectoral fins in the Sharks and Dogfishes. 
This bone is thickest at the apex, which is rounded, and thins 
out towards the distal So margin or base. The large 
longitudinal groove at the root of the spine probably corre-. 
sponds to the lower or anterior margin of this bone; or it may 
_ be that it was fitted to a lower carpal which was coadjusted 
to this bone but, being entirely cartilaginous, has disappeared. 
However this may be, it can scarcely be doubted that this 
* Poissons Fossiles, vol. iii. tab. 5. figs. 4, 5, 6. 
