166 EDWARD PHELPS ALLIS, JR. 
of the primary lip continues dorso-posteriorly along the lateral 
edge of the palatoquadrate, there forming the floor of the naso- 
buecal groove. This latter groove certainly includes, as in the 
Plagiostomi, a nasal-flap furrow, the mesial edge of which forms a 
crease beneath the rounded fold arising where the superficial 
portion of the primary lip turns outward to coalesce with the 
aboral premaxillary lip. Immediately posterior to this point the 
lateral edge of the palatoquadrate is overlapped by,a little pro- 
jecting point on the lateral edge of the mandibular dental plate, 
shown in Dean’s figure 102, (06) of this fish, this point cutting 
slightly into the primary lip. 
The rounded fold formed by the coalescence of the primary 
and aboral premaxillary upper lips runs at first aborally, and 
hence in the direction of the mesial edge of the nasal-flap furrow 
of the Plagiostomi, and then turns posteriorly (absymphysially), 
approximately parallel to the lateral edge of the palatoquadrate, 
and forms the oral edge of the postero-lateral nasal aperture. 
At its dorso-posterior end this fold is continuous with the dorsal 
end of a transverse ridge on the internal surface of the large 
naso-labial fold, to be described later, which lies, when the naso- 
labial fold is closed, in a nearly vertical position and hence 
diverging posteriorly at an angle to the oral edge of the postero- 
lateral nasal aperture. The aboral edge of the latter aperture 
begins along the anterior (symphysial) edge of the transverse 
ridge on the internal surface of the naso-labial fold, and, running 
antero-ventrally, forms the oral edge of the large valvular proc- 
ess, to be described below. When the naso-labial fold is closed, 
the summit of the transverse ridge rests against that part of the 
primary lip which forms the floor of the naso-buccal groove, and 
in that position it forms a wall which closes the passage from 
the postero-lateral nasal aperture into the buccal cavity while 
still leaving a free passage through the aperture into the nasal 
pit, and also from the aperture into a canal between the naso- 
labial fold and the external surface of the valvular process. 
Immediately posterior to the point where the transverse ridge 
on the internal surface of the naso-labial fold reaches the oral 
edge of that fold, a normal secondary upper lip begins, and from 
