162 EDWARD PHELPS ALLIS, JR. 
either a complete ring or anywhere fused with the edge of the 
nasal capsule. 
In my specimen of Heterodontus francisci the fenestra nasalis 
is, as already stated, a long and relatively narrow opening, and 
the nasal capsule is relatively deep. The oral and mesial walls 
of the capsule are largely membranous, much as shown in Gegen- 
baur’s figure 2, plate 16, but unfortunately this membrane had 
been dissected away along the edge of the ala nasalis before my 
attention was called to the importance of preserving it, and I 
can not tell whether it extended to that cartilage, as Gegenbaur 
states, or not. The conditions in the other Plagiostomi ex- 
amined would however indicate that it did not. The median 
raphe of the Schneiderian membrane lies in the line of the long 
axis of the fenestra nasalis, and the folds of that membrane are 
so long that they extend outward almost to the inner edge of 
the ala nasalis. The membrane is, as in the other Plagiostomi, 
attached to the ala nasalis, and it is so closely applied to the 
inner surface of the cartilaginous portion of the fenestra nasalis 
that where it projects beyond the fenestra it appears as an 
outward membranous extension of the walls of the nasal cap- 
sule, and this may be what led Gegenbaur to conclude that the 
membranous portions of the capsule are directly attached to the 
ala nasalis. 
The ala nasalis is, in my specimen, a complete ring, the 
postero-mesial portion of which is thin and flexible, and it 
is completely fused at one point with the outer edge of the 
nasal capsule. The processes a and 6 are as described and 
figured by Gegenbaur and Daniel, and there are projecting 
mucous folds which form the nasal valve and its seat, but they 
are without cartilaginous support. The incurrent passage is 
directed orally, passes through that part of the alar ring which 
lies lateral to the processes a and £, and leads to the postero- 
lateral end of the fenestra nasalis. The excurrent passage is 
directed from without aborally, passes through that part of the 
alar ring which lies mesial to the processes a and 6, and leads to 
the antero-mesial end of the fenestra nasalis. The little process 
of cartilage, shown in my figure projecting laterally from the 
