from the Shales of the Northumberland Coal-field. 269 



must be placed considerably apart from each other, and not 

 much in advance of the posterior margin of the nasal bone ; at 

 least it is only a short way in front of the posterior mucus- 

 groove. 



There are five or six conical teeth in each premaxillary ; 

 they are stout, grooved, and circular at the base, with the 

 crown compressed in the direction of the length of the jaw ; 

 they are provided with wide cutting-edges, and are rather 

 abruptly pointed. The largest are upwards of half an inch in 

 length, allowing for their lost apices. The three anterior are 

 much larger than the rest, and they are placed at some little 

 distance apart, there being large depressions between them in 

 the alveolar groove, apparently for the reception of the crowns 

 of the mandibular teeth. The two or three posterior teeth are 

 comparatively small, and are placed nearer together than the 

 anterior. 



Two specimens of the anterior portion of the left mandible 

 have also occurred, the largest and best preserved of which 

 is four inches long and about two and a quarter inches wide. 

 The surface exhibits the same ornamentation as the other 

 bones. The symphysial sm'face is perfect ; it is considerably 

 longer than the width of the ramus, being extended by a pro- 

 cess from the inner or lower margin of the bone ; there is a 

 trace of a mucus-groove along the inferior border of the ramus. 

 None of the teeth in these specimens are perfect ; but enough 

 is left to show that they are similar to those already described. 

 The first tooth is small, and is placed close to the symphysis ; 

 the second is very large, and is immediately behind the first ; 

 it is half an inch in diameter at the base ; a large depression, 

 five-eighths of an inch wide, succeeds this, and then four small 

 teeth placed close together, the two posterior of which are 

 larger than the anterior pair; but one of them is indicated 

 only by a mere fragment of dentine ; then comes another large 

 depression, half an inch wide, but whether or not this is for 

 the reception of the crown of a maxillary tooth, or is the im- 

 pression of the base of a tooth belonging to the mandible, it is 

 difficult to say. Close to this depression is the base of another 

 tooth equal in size to the large anterior one. At this point the 

 alveolar groove is broken away ; and shortly after, the fragment 

 of the ramus terminates. The alveolar groove is distinctly 

 defined, but widens inwardly to accommodate the bases of the 

 large teeth, which consequently have the appearance of being 

 placed within the smaller ones ; they form, however, with the 

 latter only a single row, and the outer borders of all are placed 

 on the same external line. The other ramus is very imper- 

 fect ; but, as far as they are traceable, the teeth have the same 

 arrangement. 



