Dr. R. H. Traquair—Carboniferous Selachii. 85 
and narrower separate teeth. Pleurodus is a well-known form, in 
which each plate is evidently due to the union, back to front, of a 
row of helodont teeth whose lateral extremities still tend to project 
free on each side. 
That the Cochliodonts all possessed dorsal spines seems highly 
probable. Those of Pleurodus have been described by Hancock 
and Atthey. 
Petalodontide. 
If we take Ctenoptychius apicalis, Ag., as the type of its genus, I 
must own that I fail to see any valid reason for separating Ctenopetalus 
from it, and even Petalodus is scarcely entitled to distinction. 
Harpacodus differs in having only one fold or plait at the junction 
of the crown and root, and it is in this genus that Mr. J. W. Davis 
proposes to include Ctenoptychius pectinatus of Agassiz. But Cteno- 
ptychius pectinatus is not provided with any “fold” of enamel below 
the crown comparable to those in Ct. apicalis, or to the single one in 
Harpacodus, while its root differs very considerably in shape, being 
divided below into a number of small rootlets, somewhat after the 
manner of Polyrhizodus. A new genus is therefore necessary for it, 
for which I propose the name Callopristodus. 
Oracanthus. 
Some time ago Mr. R. Craig, of Langsyde, Beith, lent me a small 
spine from the shale above the 9-inch coal at Broadstone, Ayrshire 
(Carboniferous Limestone series), which is apparently undescribed. 
It is small, flattened and broadly triangular, the anterior margin being 
1 inch in length, the posterior 12, the base } inch in breadth. The 
apex ends in a sharp spike, and just below this on the posterior 
margin are two others directed backwards. Externally the surface 
is ornamented with distinct furrows running parallel to the anterior 
and posterior margins, consequently tending to radiate from the apex 
towards the base, and giving the surface a feebly ribbed appearance. 
On these ribs are small tubercles, irregularly placed towards the 
apex, then becoming arranged in lines which proceed obliquely, or 
with a slight sigmoid curvature, across the surface from behind down- 
wards and forwards. I have seen other specimens of the same spine 
from the Carboniferous Limestone “ Bone-bed ” at Abden, Fifeshire, 
collected by Messrs. W. Anderson and W. Tait Kinnear, which show 
that the walls were thin and the spine consequently extremely 
hollow. In these specimens the external ribbing is also feeble, and 
the tubercles more thickly placed. 
In their general configuration and in the nature of their surface 
ornament, the resemblance of this spine to Oracanthus is obvious, 
although the posterior area is not so sharply defined, and though 
neither of the sides is notched or sinuated on the lower margin as is, 
so far as my observation goes, usually the case in the genus mentioned. 
It has, perhaps, still thinner walls than in the typical Oracanthi, and 
might on that account be referred to St. John and Worthen’s genus 
Pnigeacanthus ; but the generic distinction of this from Oracanthus is 
doubtful. No Oracanthus has hitherto been described with spikelets 
