On the Fossil Fishes of the Carboniferous Limestone Series of Great Britain. 417 
surface backwards into the mouth. A series of three of these is represented in 
Pl. LV., fig. 4. They probably, judging from their form and arrangement, occupied 
the space between the median line of the palate and the large teeth arranged on each 
ramus of the jaw. Whether the teeth were similarly arranged in both jaws it is 
impossible to say, but it appears probable that they were; the only difference 
observed in the teeth being in the disposition of the coronal surface ; in some 
specimens the crown is worn by attrition quite hollow, whilst in others it is rounded 
and convex though evidently much used. 
The above observations may perhaps be summarized as follows: that a row of 
three principal teeth increasing in size backwards were attached to each cartilaginous 
ramus of the jaw; that the diameter of the jaw, as indicated by the groove 
or channel on the under-surface of the teeth, diminished towards the symphysis ; 
that a long, narrow tooth was placed in front of the anterior one, and that a series 
of at least three Helodoid teeth were placed behind it, extending over the palate and 
increasing in size backwards. 
The dentition of Deltodus, Deltoptychius, Peecilodus, and the remaining genera 
were arranged, with varying modifications to suit their several forms, in ap- 
proximately close relationship to those already mentioned. The form of the teeth 
in the upper and lower jaws respectively in Deltoptychius and Deltodus somewhat 
resemble each other in general characters but are altogether distinct in detail. 
The teeth of Deltoptychius acutus were probably arranged very similarly to those 
of Cochliodus, being closely related in form so far as the teeth of the lower jaw are 
concerned. The teeth of both the upper and lower jaws are hollowed on the 
inferior surface and show the direction in which they were attached to the jaws. 
The teeth of Deltodus and Deltoptychius here ascribed to the upper jaw, appear 
to have had only one tooth to each ramus of the jaw, in this respect being similar to 
Ceratodus. It is possible that both jaws of Pcecilodus were furnished in a similar 
way. 
It is interesting to note that Professor Agassiz (“ Poiss. Foss.,” Vol. III., p. 118), 
speaking of the genus Cochliodus, describes a jaw with the teeth attached in their 
proper places. The specimen was formerly in the collection of Captain Jones, and 
is now in that of the Earl of Enniskillen by whom it was placed at the disposal of 
Professor Agassiz; it is represented in pl. 19, fig. 14, of the “ Poissons Fossiles,” 
and is regarded as being “of the greatest importance tothe history of the Cestracionts 
of the older formations, for not only does it serve to solve all doubts on the subject 
of Psammodus, but I have acquired, in seeing it, the confirmation of the supposition 
I had formed on the subject of the genus Ceratodus, which I have always believed 
should be regarded asa Squalus, having only a single large dental plate, instead of 
several ranges of teeth upon each branch of the jaw. The fragment in question 
not only supports this opinion, but it constitutes a type intermediate between 
Ceratodus and the Cestraciontes, living and fossil.” The new genus Cochliodus 
83U2 
