LIPS AND NASAL APERTURES IN FISHES 171 
been pulled upward through the hind end of the labial fold, and 
its ventro-anterior end, instead of its dorso-posterior end, lies in 
the hind end of that fold. 
The nasal apertures of Chimaera are separated from each other 
by a stout broad valvular process, already several times referred 
to, which projects ventro-antero-mesially from the aboral margin 
of the nasal pit. The external surface of this valvular process is 
concave, and its outer end is also concave or V-shaped, this end 
fitting against a corresponding surface on the dorso-lateral 
corner of the thick premaxillary lip of the fish, which forms the 
valve-seat process. On the internal surface of the valvular proc- 
ess there is a longitudinal ridge which fits into a corresponding 
depression on the premaxillary lip, a second valvular surface 
thus being formed which Jies ventro-lateral and internal to the 
V-shaped valvular surface. Because of the markedly concave 
external surface of the valvular process, a relatively large passage 
is left between it and the overlapping naso-labial fold, which 
communicates at one end with the postero-lateral nasal aperture, 
and at the other end with both the antero-mesial aperture and 
the exterior. This passage is so large that it would seem as if 
it must give regular passage to water, either incurrent or excurrent 
but exper!ments on the living fish can alone decide this. The 
posterior edge of the valvular process is formed by a delicate 
fold of mucous tissue which encloses a delicate piece of cartilage, 
the cartlage ‘1’ of Hubrecht’s (’77) descriptions. There is, in all 
my specimens, a small teat-like eminence on the mesial wall of the 
antero-mesial nasal aperture, the possible significance of which 
will be explained later. 
The antero-mesial nasal aperture is encircled by the cartilage 
‘kn’ of Hubrecht’s descriptions of Chimaera monstrosa, called by 
him the ‘Nasenmuschel’ and certainly corresponding to some part 
of the ala nasalis of the Plagiostomi. In Chimaera colliei, this 
alar cartilage has the form of an oblique section of a cylinder, the 
axis of the cylinder lying approximately in the line of the 
trabeculae and hence at a marked angle to the plane of the 
fenestra nasalis, this giving to the cartilage the appearance of 
having been pulled forward and upward, almost completely out 
