LIPS AND NASAL APERTURES IN FISHES 155 
veloped in relation to it. The oral limb of the ala nasalis is not 
prolonged mesially beyond the process 8, this apparently being 
related to the presence of a naso-buccal groove, but the aboral 
limb of the ala nasalis is thus prolonged beyond the process a 
and there sends a second long process into the nasal flap, this 
process and the process a both being thin and flexible. The line 
joining the centers of the external nasal apertures is more nearly 
parallel with the median raphe of the Schneiderian membrane 
than in Mustelus, and the current of water passing through 
the nasal pit does not have the markedly zig-zag course which 
it has in that fish. 
A secondary upper lip is found in normal position in this 
fish, and extends from the secondary angle of the gape to the 
lateral edge of the naso-buccal groove, where it ends abruptly 
against the lateral wall of the groove. The crest of the fold of 
this lip runs directly toward the process 8, which lies in the line 
of the fold, and a well marked crease, extending from the line of 
the angle of the gape about half way to the process £8, cuts 
across the definitive lip and separates the crest of the fold of the 
secondary upper lip from the primary lip. The nasal flap 
extends to the upper edge of the mouth, completely covering 
both the postero-mesial nasal aperture and the naso-buccal 
groove, and its oral edge has the appearance of forming a part of 
the secondary upper lip. It, however, forms no part of the fold 
of that lip, as comparison with Miiller and Henle’s (’41) figures 
of Scyllium edwardsii, Scyllium catulus, and Seyllium africanum 
will show, for in these several fishes, notwithstanding that the 
oral edge of the nasal flap lies not far from the upper edge of the 
- mouth, the fold of the secondary upper lip runs forward, without 
interruption, oral both to the nasal flap and the nasal apertures, 
exactly as it does in Chlamydoselachus and Mustelus. There 
is no naso-buccal groove in either of these three species of 
Scyllium, the presence of this groove in Scyllium canicula thus 
being related to a nasal flap which extends to the upper edge of 
the mouth, or, more properly, to the presence of a nasal-flap 
furrow which has that extent, that furrow lying beneath the 
nasal flap (Allis, 716). 
