from the Shales of the Noi'thumherland Coal-field. 351 



All the bones of the jaws frequently occur detached. A 

 large series of such have been procured, many of Avhich are 

 associated with the scales of the fish. The anterior laniary 

 teeth are nearly always present in both the pra3maxilla3 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 border 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 pretty 

 regularly wedge-shaped, the posterior exti-emity being pointed. 

 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 pr^emaxilla. These, however, are not 

 always to be seen ; and the posterior laniary teeth are very 



