310 Mr. T. Atthey on Ctenodus obliquus. 
Ctenodus, corresponding exactly as it did in conformation to 
the articular bone of the recent Ceratodus. 
Last year (1874) I was fortunate enough to find, also at 
Newsham, two fine specimens of Ctenodus obliquus with this 
very articular bone 7m situ; and one of these is figured on 
Plate XIX. figs. 1 and 2. 
The bones differ in size, being from # of an inch to 
4 inches in length. The inner side of the mandible is 
formed by the ramus or body of the jaw surmounted by the 
teeth; and these at their upper margins are turned outwards 
and flattened, and project towards the upper border of the 
articular or external piece. The narrow elongated space left 
between the two bones of the fossil at this part would neces- 
sarily in the fresh state be filled with connective cartilage and 
ligament, just as the corresponding space is in the recent 
Ceratodus Forstert. 
The articular bone of Ctenodus is of about the same length 
as the inner plate or ramus which bears the teeth, slightly 
convex on the outer surface, and marked by five or six aper- 
tures for vessels ; it is pointed upwards in front like the prow 
of a boat. Its posterior border presents two scallops, the 
upper somewhat larger than the lower, which extends to the 
posteriorly projecting point of the lower border, which is 
convex; the upper scallop ends at a rounded projection, which 
separates it from the upper border. This border presents two 
shallow concavities, the anterior occupying the greater part of 
the border; the posterior has a projection on its inner side, 
somewhat in the form of a bracket, for the support of the 
teeth of the inner plate or ramus. 
On a thin slab of shale from Newsham in my possession, 
and which measures 5 by 34 inches, are seen imbedded one 
rib, several bones of the head, fragments of scales, and what 
I take to be right and left vomerine teeth of Ctenodus, one of 
which is figured on Plate XIX. fig. 4. The teeth are 54, of 
an inch broad, and thick at the base—their outer surfaces 
being slightly convex and their inner slightly concave, the 
two surfaces converging from the base to the thin, convex, 
serrated or toothed margin, which is ;%, of an inch long. The 
microscopic structure of these teeth corresponds exactly with 
that of the maxillary teeth of Ctenodus. 
I possess about a dozen other specimens believed to be 
vomerine teeth of Ctenodus, in close proximity on the same 
slabs to the bones of the head and teeth of Ctenodus ; some of 
these are a little larger, others a little smaller, than the two 
above described. 
