MAXILLARY AND VOMER BONES OF POLYPTERUS 351 
labials of the Selachii. Teeth could, however, evidently have 
been developed in relation to any other firm underlying support 
found in the region included between the primary and secondary 
upper lips, for, that whole surface having been primarily a part 
of the external surface of the head, no one part of it was probably 
better suited than another to the production of teeth. The 
maxillary teeth of Polypterus would then not necessarily belong 
to the primary dental arcade, and hence be dermopalatine ones, 
as I formerly concluded, simply because they occupy a position 
definitely internal to that of the teeth of Amia. 
This view of the subject has led me to reexamine my Polypterus 
material, and as I find that the labial folds and furrows of that 
fish were not properly identified in my earlier work, they will be 
fully redescribed after first describing the condition in Acanthias, 
specimens of which I have received since my recent work (Allis, 
18) was sent to press, and also those in Amia. The conditions 
in Lepidosteus, Polyodon, and certain of the Teleostei will then 
be considered, and the maxillary bones of these several fishes 
then compared with those in certain of the early fossil fishes. 
ACANTHIAS BLAINVILLII 
In this fish (figs. 1 and 2) the labial fold of either side extends 
dorso-anteriorly beneath the supralabial fold, and the latter 
fold, pressing upon the labial fold, separates from its oral edge a 
smaller fold which is all that is seen in external views. This 
smaller fold encloses the anterior upper labial, and as it is repre- 
sented, in Polypterus and certain of the Teleostei, by a flap-like 
structure, it may be called the maxillary labial flap. The slight 
furrow that, in Acanthias, separates this fold from the remainder 
of the labial fold is then the maxillary labial-flap furrow, and it 
runs anteriorly into the supralabial furrow. The supralabial 
furrow has, as stated in my earlier work (Allies, ’18), supra- 
labial and postlabial portions, and my present work shows that 
these two parts of the furrow are, in certain fishes, distinctly 
different morphological structures. 
In the lower jaw there is a mandibular labial flap and a labial- 
flap furrow similar to those in the upper jaw, but much more 
