Dr R. H. Traqioair on Chondrosteus acipenseroides. 357 



maxilla to Chondrosteus. But an examination of the original 

 specimen represented in pi. Ixix. of his memoir shows that 

 his " pnemaxilla" is the suborbital bone, and that his maxilla 

 — the small bifurcate bone behind it — appertains to the 

 palate, and will be described immediately as a pterygoid 

 element ! The real maxilla in this specimen is interpreted 

 by Sir Philip as a mandible, while to this jugal plate he has 

 assigned the name and position of hypotympanic ( = quadrate). 



Within the space bounded by the maxillae, the roof of the 

 mouth is principally composed of two plates ( m.'pt., Figs. 2 

 and 4) of a somewhat oval or ovoid contour, narrower behind 

 than in front. Anteriorly, these plates are placed behind 

 the symphysis of the maxillae ; mesially, they articulate with 

 each other along a portion of their internal margins, while 

 externally each comes into contact with the maxilla of its 

 own side for the anterior half of its length, behind which the 

 margin recedes inwards, the little bone pt. being placed just 

 where the recession takes place. These plates were recog- 

 nised by Sir Philip Egerton as "palatine," and are un- 

 doubtedly the representatives of the two plates occupying a 

 corresponding position in Acipenser, and which, although 

 formerly usually reckoned as " palatines," are designated as 

 " pterygoids " by Prof. W. K. Parker.^ To my mind it seems 

 to correspond more with the mesopterygoid of other fishes, 

 and I have lettered it accordingly. 



Placed at the middle of the outer edge of this last described 

 bone, and articulating both with it and with the maxilla, is 

 a small bone (pt.) which bifurcates posteriorly, one limb 

 being placed along the maxilla, the other along the meso- 

 pterygoid 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 rela- 

 tions 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 

 hehind the suhorbitcd, we may feel a little surprised at the 



^ O}). cit., p. 172. 



