44 Dr. R. H. Traquair on the 
vascular ins their nature and of the same essential character 
as those on the inserted portion of a Selachian spine, only not 
so regularly parallel as is usually the case in the latter. On 
making microscopic sections, transverse and longitudinal, 
through the substance of the supposed “carpal bone,” it is 
found to be completely traversed by a close network of 
vascular or Haversian canals, the canals in some parts en- 
larging so as to give a rather more open character to the 
tissue than is found in the internal part of a Gyracanthus- 
spine itself, while the ground-substance, hard and calcareous, 
is permeated by minute branching and anastomosing tubules, 
which are frequently seen to radiate from the vascular canals. 
This is not, however, the structure which Selachian cartilage 
assumes when calcified or “ ossified’’* ; on the contrary, if 
the tissue be not vascular dentine, it is certainly very like it. 
I am therefore of opinion, that the bodies in question have 
nothing to do with “ carpal bones,”’ or with the endoskeleton 
of a shark at all, but that they were, on the other hand, 
dermal appendages, which may probably enough have been 
situated in the neighbourhood of the pectoral fin, the thin or 
open side being proximal and the apex distal. The want of 
enamel, or of sculpture on any part of the surface, shows 
that they must have been covered with a thin layer of skin. 
Their frequent occurrence in close relation to the spines of 
Gyracanthus yenders it, indeed, highly probable that they 
belong to the same fish. 
I hope, on a future occasion, to enter more minutely into 
the microscopic structure, both of these bodies, and of the 
Gyracanthus-spines themselves. 
3. On two new Species of Gyracanthus. 
In the ‘ Geological Magazine’ for last month (Nov. 1883) 
I have given brief diagnoses of two new species of this genus 
from the Carboniferous Limestone series of Scotland, concern- 
ing which I propose, in the present communication, to enter a 
little more into detail. 
Gyracanthus nobilis, Traquair. 
Gyracanthus tuberculatus, Traq. Geol. Mag. dec, ii. vol. viii, 1881, 
p. 34. 
Gyracanthus nobilis, Traq. ibid. dec. ii. vol. x. 1883, p. 542. 
The spines which I have named Gyracanthus nobilis are of 
* For an account of the structure of calcified Selachian cartilage, see 
Williamson on the “Structure and Development of the Scales and Bones 
of Fishes,” Phil. Trans. 1851. 
