REMAINS OF REPTILES AND FISHES. 71 



the alveolar groove is broken away ; and shortly after, the frag- 

 ment of the ramus terminates. The aveolar 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 imperfect ; 

 but, as far as they are traceable, the teeth have the same arrange- 

 ment. 



Besides the above, we have also obtained from the same loca- 

 lity portions of three other mandibles : one belongs to the left 

 ramus, and is in a bad condition ; two are in a good state of pre- 

 servation, but, unfortunately, they both represent the same por- 

 tion of the right ramus, the anterior part of each being wanting, 

 as also the proximal extremity. They each measure about six 

 inches in length, and widen a little backwards, where they are 

 2|- inches broad. If we add to the length of these fragments 

 that of the anterior portion before described, and allow for the 

 parts that are wanting, it would appear that the ramus could not 

 be less than 12 or 18 inches long. The internal cartilage having 

 been removed, the lateral bony walls have collapsed and are in- 

 clined inwards. The jaw is consequently comparatively thin and 

 flattened. The external surface exhibits the peculiar ornamen- 

 tation in a very beautiful manner. It is the same as on the other 

 bones, the sculpturing extending over the whole surface in the 

 form of smooth elevated ridges composing an irregular reticula- 

 tion, with the meshes or depressed spaces deep and of various 

 forms, frequently angular, sometimes rounded, but most com- 

 monly elongated ; so that the reticulated ridges, on the whole, 

 have a somewhat dendritic appearance. This striking embossed 

 ornament closely resembles that of Lahyrinthodon Jeptognathus 

 and L. pa^chygnathus ; only it is considerably finer.* The inner 

 surface of the bone is smooth, as well as the external border of 

 the alveolar ridge ; and there is a groove along the lower mar- 

 gin extending the whole length of the fragment. 



♦See Prof. Owen's Paper, "Transactions" Geological Society, Ser. 2, Vol. VI., Plate* 

 XLIII., XLVI. 



