DAVIS : FOSSIL FISH REMAINS. 
57 
quietly in position ; at the anterior extremity ten or twelve 
teeth indicate the position of the head. Supposing the number 
of teeth to have been twelve, there would be three to each ramus 
of the jaw, which is the same number as in the Cochliodonts. The 
teeth of Pleurodus are not unlike those of Poecilodus in form, 
and surface configuration, and it is within the range of possibility 
that there may be some relationship between the members of the 
Cochliodont group and Pleurodus, though it may be advisable to 
\vithhold a detailed expression of opinion until more extended 
observations shall have been made. 
The representative of the Psammodontidae occurring in 
Yorkshire are not numerous, and are small compared with those of 
Bristol and Armagh. They possess the usual characteristics of 
the group, and formed a flat pavement-like arrangement in the 
mouth admirably adapted for crushing the hard coatings of tes- 
taceous animals. Prof, de Koninck in his description of the Fossil 
Fauna of Carboniferous Limestone of Belgium, has suggested that 
the teeth were arranged so as to cover the whole of the palatal 
surface of the mouth ; the square massive teeth being joined at 
their edges, and having on each side and in front smaller teeth, in 
some cases somewhat triangular in outline, to fill up the rounded 
conformation of the jaws. 
Associated with the Psammodonts are smaller teeth, similar 
to them in being flat on the surface, but dissimilar in other respects. 
They were named by Prof. Agassiz, but not described, as Dimy- 
leus Woodi, from specimens contributed by the late Mr. Wood of 
Richmond in Yorkshire, to the Enniskillen collection. At Armagh 
many other genera of fish-teeth have been found, which closely 
approximate with those of Dimyleus found in Wensleydale. A 
careful study of the whole group shows that they are distinct from 
the Psammodont family. They have therefore beeu grouped to- 
gether as a distinct family, Copodus being regarded as the typical 
genus, they are termed the Copodontidge. 
Perhaps the most remarkable group of fish-remains found in 
