Dr. R. H. Traquair — On Chondrosteus acipenseroides. 255 



"bone {pt.) "which bifurcates posteriorly, one limb being placed 

 along the middle, the other along the mesopterygoid palate-plate. 

 This is the bone which Sir Philip Egerton has interpreted as 

 "maxilla" {op. cit. pi. Ixix. 21), but whose true relations are most 

 clearly seen in a large number of specimens in the British Museum. 

 These relations are not obscure even in the specimen figured by 

 Sir Philip ; but here, as already explained, he unfortunately mistook 

 the real maxilla for the lower jaw. As the position of this little 

 bone is about the middle of the maxilla and behind the suborbital, 

 we may feel a little surprised at the following statement in the 

 published abstract of Mr. Davis's paper : — ■" From the position of the 

 respective maxillary and premaxillary bones in this (Mr. Davis's) 

 specimen, there can be no further doubt that the small bifurcated 

 bone of C. acipenseroides, Ag., described as the maxillary bone, is 

 really the premaxillary." 



Fig. 5. — Profile of head of Chondrosteus, restored. 



But if we inquire what this little " bifurcated bone " really 

 is, I answer that it seems to me to occupy, as regards the maxilla 

 and the great palate-plate, a position quite analogous to that of the 

 small bone in Acipenser lettered as " palatine " by Professor W. K. 

 Parker, but which I have come to look upon as a pterygoid or 

 ectopterygoid, for the same reasons which have induced me to regard 

 the great palate-plate as a mesopterygoid, and as such I have 

 accordingly marked it. 



I have seen no evidence of ossified quadrate or metapterygoid 

 elements. There can be no doubt that the bone interpreted by Sir 

 Philip Egerton as a combined "mesotympanic" and "hypotympanic" 

 {symplectic and quadrate of modern nomenclature), is that external 

 plate appended to the hinder extremity of the maxilla, which I have 

 already described as the jug al. 



The mandible is stout, and anteriorly is, like tbe maxilla, strongly 

 cm-ved inwards to meet its fellow of the opposite side in a symphysis: 

 its outer surface presents a well-marked longitudinal groove, which 



