184 EDWARD PHELPS ALLIS, JR. 
lips, are found only in the antero-mesial portions of the lips of 
the Plagiostomi, and probably also in those of the Chondrostei. 
The secondary lips are probably found in the postero-lateral 
portions of the lips of the Chondrostei; are found either in the 
corresponding portions only of the lips of the Plagiostomi, or 
extending the full length of the gape of those fishes; extending 
the full length of the gape in all of the Teleostei, Holostei and 
Crossopterygii that I have been able to examine; and extending 
the full length of the gape in the lower jaw of the Holocephali, 
but not the full length of the gape in the upper jaw. 
The secondary upper lip passes between the upper edge of the 
mouth and the nasal apertures in all of the Teleostei, Holostei 
and Crossopterygii that I have been able to examine, as it also 
does in the Chondrostei, if there present. In all of the Plagios- 
tomi that I have been able to examine in which there is no 
naso-buccal groove, excepting only Heterodontus, the secondary 
upper lip also passes between the upper edge of the mouth and 
the nasal apertures; but in those of these fishes in which there is 
a naso-buccal groove, the lip either abuts against the groove 
and ends there (Scyllium), or runs along the lateral edge of the 
groove (Raia); the naso-buccal groove resulting from the en- 
‘ counter of the fold of the secondary upper lip with the postero- 
mesial (oral) nasal aperture. In Heterodontus the secondary 
upper lip passes between the two nasal apertures and is con- 
tinued mesial to those apertures as the so-called fronto-nasal 
flap, or process. In the Holocephali this lip is represented in 
the oral edge of the labial portion of the naso-labial fold, and it 
was primarily interrupted by its encounter with the postero- 
mesial nasal aperture, as it is in those of the Selachii in which a 
naso-bucecal groove is found. : 
The tertiary lip is found only in the Dipneusti, and even there 
only in the upper jaw, the lip passing aboral to both the nasal. 
apertures. In adults of the Holocephali and Teleostomi (ex- 
cepting the Chondrostei), and probably also in embryos of 
Acipenser, this tertiary upper lip of the Dipneusti is represented 
in a fold of the dermis on the external surface of the head which 
is the supramaxillary fold of the present descriptions. 
