from the Shales of the Northumberland Coal-field. 351 
All the bones of the jaws frequently occur detached. A 
large series of such have been procured, many of which are 
associated with the scales of the fish. ‘The anterior laniary 
teeth are nearly always present in both the premaxille and 
mandibles; but the additional large teeth of the latter are 
seldom present. In four or five instances, however, they are 
distinctly displayed ; and in one specimen there are five laniary 
teeth, including the anterior one, 
In the detached state the form of these bones can be well 
observed. The maxillaries are usually seven-tenths of an inch 
long and about three-tenths of an inch wide at the broadest 
part. They are flat thin bones, produced and pointed in front, 
and widened rather suddenly behind, as already stated; the 
alveolar border is nearly straight; the upper naps Be in front is 
parallel with the alveolar border for some little distance back- 
wards ; it then suddenly ascends to the posterior margin, which 
slopes backwards and downwards. ‘There is, at a little dis- 
tance from the anterior extremity, a well-developed narrow 
articular process, which stretches upwards and forwards. The 
teeth vary somewhat in number; there are usually about 
twenty-five, which are arranged along the alveolar margin in 
regular order. This regularity, however, is frequently dis- 
turbed by the approximation of two or more; sometimes three 
or four are placed close together. 
The premaxillaries are long narrow bones, about as long as 
the maxillaries, being usually seven-tenths of an inch in length 
and nearly three-tenths of an inch broad; the alveolar margin 
is almost straight; the opposite margin gently slopes back- 
wards in a somewhat sinuous course; so that the bone is prett 
regularly wedge-shaped, the posterior extremity being feeb § 
There are about the same number of teeth as in the maxilla, 
with the addition of a large conical laniary tooth in front, im- 
mediately before which is a small tooth or two. 
_ The mandibular bone we have never seen quite perfect: 
one of the most complete in the series measures one inch and 
four-tenths in length, and about two-tenths of an inch wide 
near the front; the upper and lower margins are nearly 
parallel ; it is rounded in front, and appears to taper a little at 
the posterior extremity ; the anterior extremity is slightly bent 
upwards. ‘There are from fifteen to twenty teeth in our frag- 
ments ; the number must be much greater in the entire ramus. 
There is likewise a large laniary tooth in front, and three or 
four others placed along the ramus, in a line within the small 
teeth ; in front of the anterior laniary there is a small tooth or 
_ two like those in the premaxilla. These, however, are not 
always to be seen; and the posterior laniary teeth are very 
