716 Davis — On the Fossil Fish- Remains of the Coal Measures of the British Islands. 



jaw witli a long straight suture extending along the median line of the palate. Its 

 broadest part is 0'14 m. The inner margin is comparatively thick, but much less 

 so than the outer margin ; the intermediate area is apparently thin, but of the 

 same chondroid or granular structure as the other portions, the usual osseous 

 centres being abundantly intermixed with the cartilaginous base. 



The wide expansion of the palato-pterygoid bone over the palate is remarkable. 

 The researches of Dr. Anton Fritsch have shown that the bone in the palatine region 

 extends high up the side of the head, diminishing anteriorly and extending to 

 the snout in a more or less attenuated form. This magnificent specimen exhibits 

 a lateral expansion from the anterior portion of the jaws, so as to form a pair of 

 osseous plates extending to the median line of the palate and there joining 

 together. In the German specimens of Pleuracanthus (Xenacanthus) Dr. Kner 

 considered that the upper jaw was divided into maxillary and premaxillary, but 

 in this specimen there is no evidence of this unless the elements at the nasal 

 extremity can be so construed. The Texas example, described by Professor Cope, 

 showed the upper jaw to consist of a single bone on each side the palato-pterygoid. 

 This view is also supported by the specimens described by Dr. Fritsch. 



The large expansion of the palato-pterygoid over the palatal area of the mouth 

 in this specimen does not extend to the anterior extremity of the jaws, but a 

 triangular area starting at a point where the two rami are most anteriorly in 

 juxtaposition, 0'08 m. from the nasal extremity, is occupied by a number of smaller 

 semi-osseous pieces mixed with numerous teeth ; these apparently completed the 

 anterior portion of the wide rounded snout, and probably represent the pre- 

 maxillary. There is at the anterior termination of the palato-pterygoid a 

 thickened concave margin which has apparently served for attachment to the 

 pieces composing the snout. The several ]jarts, however, are not so well pre- 

 served as to enable a reproduction of the natural arrangement to be made 

 (PI. Lxv., fig. Ice). This peculiarity is indicated in the specimen described 

 by Dr. Jordan in the Neues Jahrbuch in 1849, and afterwards figured by Dr. 

 R. Kner,* in which the under surfaces of the upper jaws are exhibited, separated 

 by a distinct interval at the anterior extremity. 



The teeth are numerous and vary considerably in form. The average length is 

 O'OiS from the base to the extremity of the denticles. The form may have borne 

 some relationship to the position the teeth occupied in the mouth, but in this 

 specimen, as in nearly all the others, the teeth are scattered in indiscriminate 

 confusion over the slab, and only a very rough estimate can be made as to their 

 original position. There are a few teeth, however, which appear to be in their 

 proper places attached to the anterior portions of the jaws. They are smaller 



* Sitzungsberichte Kaiser. Akad. Wiss. Wien, vol. Iv., pt. i., p. 568, pi. vi., fig. 1. 1867. 



