156 EDWARD PHELPS ALLIS, JR. 
The naso-buceal groove of Scyllium canicula is short, the 
postero-mesial edge of the nasal. capsule lying not far from the 
upper edge of the mouth. The groove is bounded laterally by the 
abruptly ending anterior end of the fold of the secondary upper 
lip, and bounded mesially by the base of the nasal flap. The 
postero-mesial nasal aperture has the full width of the naso- 
buccal groove, and, as the passage leading from the nasal pit to 
this aperture is always directed orally, the oral edge of the 
aperture must have lain primarily near the upper edge of the 
mouth. It is therefore this edge of this aperture that primarily 
interrupted the fold of the secondary upper lip as it pushed for- 
ward toward the symphysis, and the encounter of the fold with 
the aperture raised the lateral edge of the aperture to such an 
extent that the oral edge of the aperture became a groove, the 
mesial edge of the groove being formed by the mesial edge 
of the nasal-flap furrow. The fold of the secondary upper lip 
could not cross the postero-mesial aperture and reappear mesial 
to it, because of the barrier formed by the nasal flap. The naso- 
buccal groove of this fish is thus not an independently developed 
structure especially designed to connect the nasal pit and the 
cavity of the mouth, as is generally assumed to be the case, but 
is simply the oral edge of the postero-mesial nasal aperture and the 
corresponding edge of the nasal-flap furrow transformed into a 
eroove by the encounter of the fold of the secondary upper lip 
with the lateral edge of the nasal aperture. 
In Raia (species not given) Gegenbaur (’72) shows the ala 
‘nasalis completely fused with the outer edge of the nasal capsule. 
In two specimens of Raia clavata I find it wholly separate from 
the capsule, but strongly attached to the inner lining membrane 
of the capsule. The process a is long and flexible and lies in the 
lateral edge of the nasal flap, as shown in the figures in my 
work on the labial cartilages of this fish (Allis, 716). On the 
internal surface of this part of the nasal flap is a large pad of 
tissue, the thicker, aboral portion of which lies directly above 
the nasal pit while the less tall, oral portion rests in a depression 
on the opposite side of the nasal opening, immediately mesial 
to the base of the process 6. The process 6 projects into the 
