364 EDWARD PHELPS ALLIS, JR. 
position, the hind end of the labial fold, in which the cartilage 
lies, forming a narrow horizontal shelf which projects posteriorly 
from the angle of the gape. Anterior to this cartilage, the oral 
edges of the maxillary and mandibular portions. of the labial 
fold lie, at first, at right angles to the cartilage, and then each 
curves gradually forward toward the anterior end of the jaw 
to which it is related. 
The maxillary and dentary bones are both somewhat scooped 
out, on their external surfaces, to lodge the related portions of 
the labial fold, this being particularly marked on the maxillary. 
No bone is found in any portion of the labial fold. The labial 
cartilage is, in my 75-mm. specimen, apparently of cartilage that 
is strictly similar to the other cartilages of the head. 
Posterior to the hind end of the labial fold, the supralabial 
and sublabial folds coalesce, excepting as they are in part sepa- 
rated by a thin web of integumental tissue, and the dorsal edge 
of the one furrow and the ventral edge of the other meet at an 
acute angle which forms what I called, in Ceratodus (Allis, 718), 
the tertiary angle of the gape. The lines that bound this angle 
in Ceratodus I considered to represent tertiary upper and lower 
lips, the upper lip alone becoming functional and forming the 
definitive upper lip of the fish. The secondary upper lip was 
said to be hardly recognizable in my specimen of Ceratodus, 
and to be found at the angle of the gape. My present work 
tends to confirm this conclusion, and I now definitely identify 
the secondary lip in the short fold shown lying immediately 
anterior to the secondary angle of the gape in the figure given 
in my earlier work (l.c., fig. 9). I, however, now find that 
the exposed lateral edge of the labial fold of Ceratodus corre- 
sponds to the ventral edge of. that part of the fold of Polypterus 
that lies posterior to the secondary angle of the gape, and not, 
as I formerly concluded (Allis, ’00), to the dorsal edge of the 
maxillary labial-flap. The labial fold of Ceratodus has accord- 
ingly not been turned upward and inward upon the roof of the 
buceal cavity, as I formerly concluded. It has simply acquired 
a permanently nearly horizontal position, similar to that in 
Polypterus when the mouth is widely opened, and has then 
