MAXILLARY AND VOMER BONES OF POLYPTERUS S10 
Chondrostei, and although it is said by him to be comparatively 
small and insignificant, it was nevertheless well developed in 
certain of these fishes. This indicates that a complete secondary 
upper lip had already been developed in these fishes, but pos- 
sibly, in certain of them, not yet markedly differentiated from 
the primary lip. In Nematoptychius greenocki, the premaxil- 
lary is shown well developed by Traquair (’77), and there in 
articular contact, posteriorly, with the anterior edges of a large 
median supraethmoid and a lateral bone on either side that is 
called both a prefrontal and an anterior frontal. This anterior 
frontal is traversed by what is apparently the anterior portion 
of the supraorbital laterosensory canal, that canal ending im- 
mediately lateral to the single nasal opening of these fishes, 
approximately in the relation to that opening that it has in 
Amia (Allis, ’89) to the anterior nasal opening. The anterior 
frontal of this fish is thus apparently a canal bone, and hence, as 
Traquair states, cannot be the homologue of the prefrontal 
(ectethmoid) of the Holostei and Teleostei. The relations of 
the bone to the supraorbital canal would seem to show that it is 
the homologue of the nasal of recent fishes, but the bone lies 
lateral to the single nasal opening, while the nasal bone of 
recent fishes lies mesial to both nasal openings. ‘There is no 
indication, in any of the Palaeoniscidae, of a posterior nasal 
aperture either mesial or lateral to this bone. 
The maxillary of the Palaeoniscidae forms a direct posterior 
continuation of the premaxillary, and hence, like the maxillaries 
of Amia and Polypterus, is definitely posterior in its relations to 
that bone. It has a narrow anterior portion and a broad pos- 
terior one. Its dorsal edge is said by Traquair (’77) to be cut 
away so as to follow exactly the contours of the suborbital and 
postorbital bones, and to be in articular contact with them and 
also with the preoperculum. It is not said that these bones 
were firmly attached to each other, but this seems implied in 
the descriptions, and they are apparently shown so attached in 
a figure of the head of Oxygnathus. In that figure the head of 
the fish has been flattened out in such a manner that the mouth 
is shown widely opened, but the maxillary nevertheless retains 
