356 EDWARD PHELPS ALLIS, JR. 
The dorsal end of the preangular crease forms the mesial 
boundary of a slight ridge, or fold, of the tissues at the dorsal 
edge of the internal surface of the labial fold, this ridge enclosing 
a ligament which extends from the internal surface of the maxil- 
lary bone, near its anterior end, to the top of the coronoid 
process of the mandible (Allis, ’97, p. 548). 
The secondary upper lip, represented in the ventral edge of 
the labial fold, is continued forward to the anterior end of the 
snout, where it is continuous with its fellow of the opposite side. 
The labial fold of Amia is thus a strictly maxillary fold, con- 
taining no mandibular component and differing markedly in this 
from the fold of Acanthias. The maxillary labial flap of the 
latter fish is also wanting in Amia. It nevertheless seems un- 
questionable that the supralabial and postlabial furrows of the 
two fishes are homologous, and, this being so, the deeper part 
of the maxillary portion of the fold of Acanthias, the part that 
encloses the posterior upper labial, must be contained in the 
fold of Amia, and it is probably represented in that little ridge 
on the internal surface of the fold of Amia that encloses the 
ligament just above referred to. The mandibular portion of the 
fold of Acanthias must then be represented either in some part 
of the mandible itself of Amia or in the fold of tissue that lies 
dorso-external to the little furrow that I have described in the 
mandible. That fold has decidedly the position and appearance 
of a labial flap, and it contains no tissues that would seem to 
represent a mandibular labial; and, furthermore, there is, in 
Amia, a tall coronoid process of Meckel’s cartilage that may, 
perhaps, represent a mandibular labial. That process is not 
found, according to Pollard (’95, p. 413), in any of the Selachii, 
and in most, if not all, of those fishes there is a mandibular labial. 
The process lies external to, or gives insertion to, all parts of the 
adductor muscles of the mandible; and its dorsal end lies pos- 
terior to, and approximately in the line of, the secondary angle 
of the gape. This process and the stout ligament that arises 
from its dorsal end and runs forward in the little ridge at the 
dorsal edge of the internal surface of the labial fold, thus have 
to each other and to the adjacent parts quite closely the relations 
