86 Dr. Rk. H. Traquair— Carboniferous Selachit. 
at the apex, but as the apices are more or less worn, a ready explana- 
tion of their absence is obtained. I therefore designate this spine 
Oracanthus armigerus, with the remark that if it be not a true 
Oracanthus, it is an excessively closely allied form. 
Mr. Davis recognizes that the spines of Oracanthus existed in pairs, 
and are not bilaterally symmetrical, having one side larger than the 
other; but when he refers them to the “ posterior termination ” of the 
body, hints at removing the genus to the “ Placodermic Ganoids,” and 
figures a whole series of really undeterminable fragments as bones of 
the head of this supposed Placoderm, we can hardly follow him. I 
have carefully gone over all the specimens in the British Museum 
which he has figured as “‘ upper jaw,” “central bone of cranium,” ete., 
and can find no evidence for such determinations. I have also 
examined microscopic sections of Oracanthus, and find that they 
consist of Selachian dentine. And we may also appeal to the 
obvious resemblance, which the spines of Oracanthus bear to the 
thin-walled triangular appendages often found associated with 
Gyracauthus. which, though not “ carpal bones,” as Messrs. Hancock 
and Atthey imagined, are unquestionably Selachian in their nature. 
The writer of a review of Mr. Davis’s work, which appeared in 
the GrotoctcaL MaGazine for November, 1883, does not believe 
that the Oracanthi formed the posterior extremity of the body of a 
Placodermic Ganoid, but that “it seems probable that they may have 
occupied a lateral position on the head of these old Elasmobranch 
fishes.” And if I am right in my determination of Oracanthus 
armigerus, sufficient corroboration of this view has now turned up. 
In the Museum of Science and Art, Edinburgh, there is a specimen 
from the Eskdale beds, showing the head of a small Selachian, 
crushed vertically, along with part of the body, the latter being, 
however, bady preserved. In the head are broken remains of 
several large flattened-convex tooth-plates, extremely Cochliodont 
in aspect, but too imperfect for identification with any known genus 
or species. But the great point of interest is that each postero- 
lateral angle of the head projects in a pointed process like the corner 
of a Cephalaspis buckler, and that process is—the spine lanes I have 
described as Oracanthus armigerus. 
I think there can be no further doubt that the position of the 
Oracanthus spines is on the head of a Selachian, and not on the tail 
of a Placodermic Ganoid. 
Addendum to Cladodontide. 
I have long been of opinion that the teeth from Borough Lee, 
which I described as Cladodus bicuspidatus, and which never show 
more than two cones, a large one and one small lateral one, which is 
absent in some specimens, ought to be included in a new genus 
distinct from Cladodus. I therefore propose for this form the name 
Dicentrodus, and venture to express an opinion that it will turn out 
to be more allied to Diplodus than to Cladodus. 
