MAXILLARY AND VOMER BONES OF POLYPTERUS BY A 
of a mandibular and posterior upper labial, and it is quite 
probable that they represent those labials. 
The maxillary bone of Amia lies in the labial fold, and al- 
though it is found in 12-mm. specimens, the teeth related to it 
do not appear until much later, when the fish is about 40 mm. 
in length, and they are implanted only along its ventral edge 
(Allis, ’00, p. 273). This bone is thus certainly not developed, 
ontogenetically, in any relation whatever to those teeth, and, in 
my opinion, it is a dermal bone strictly similar, in origin, to the 
bones that cover the cheek of the fish. That it may have been 
primarily developed in some relation to underlying labial car- 
tilages is possible, but it seems to me improbable. The teeth 
that later become implanted upon it were, however, quite 
probably primarily developed in relation to an anterior upper 
labial, for the primordium of that labial must lie in the ventral 
portion of the labial fold. That these teeth and the dermal plate 
on which they are actually implanted were primarily independent 
structures would seem to be further shown by the conditions 
found in most of the Teleostei, for, in those fishes, the dental 
component of the bone of Amia has become attached to the hind 
end of the premaxillary, and forms a posterior prolongation of 
that bone, the dermal component of the bone of Amia becoming 
an independent and always non-dentigerous maxillary. 
The maxillary and premaxillary teeth all issue from the 
secondary lip slightly internal to its ventral edge, and there is 
no sulcus formed external to them. The maxillary teeth are 
much smaller than the premaxillary ones, and seem to be a 
later and wholly independent acquisition. The premaxillary 
teeth have the appearance of completing the pterygopalatine 
arcade; as if they had primarily occupied the existing interval 
between the dermopalatine teeth of opposite sides, and had 
then been carried bodily forward onto the ventral edge of the 
secondary upper lip, as seen in my figures of this fish (Allis, 
98). But if this had been the case, the fold that I consider 
to be the primary upper lip would evidently be formed by the 
palatine fold of Acanthias, and that cannot be, for the fold of 
Amia is continued posteriorly external to the external edge of 
