8 BULLETIN OF THE 
alone it is doubtful whether close affinities would be suspected. In the 
Notidanidz the articulations of the jaws are as far back as in any of the 
Galei, but even in them the jaws pass little behind the skull, while in 
the majority of the other Selachia the suspensorium, or hyomandibular, 
is directed downward, outward, or forward. 
The skull of the frilled shark is suggestive of immaturity ; the thin 
walls, soft cartilage, and large pores and foramina with thin edges around 
them, seem to be those of a young, rather than an adult specimen. 
Compared with that of Heptabranchias it agrees better with an embryo 
than an adult. Looking at it from above, its shape may be likened to 
that of the body of a guitar, the vertebral column answering to the neck 
of the instrument, and the narrow section between the orbits to the 
middle of its box. Across the nasal capsules the width is nearly two 
thirds, and across the interorbital space nearly two fifths of the length. 
The walls are very thin. In longitudinal section the thickness of floor 
and roof is comparatively uniform. There is a marked contrast in this 
respect if compared with skulls of Hexanchus and Heptabranchias, in 
which these portions are thick and irregular (see Gegenbaur, Das Kopfs- 
kelet der Selachier, Pl. IV. figs. 1 and 2). The roof is not very convex, 
nor is it to be called very irregular. Behind the front teeth the floor 
makes a sharp bend upward, which allows the jaws and teeth to rest 
nearly at the level of the bottom of the skull. The chamber is large, 
and the brain small. The rostrum (a) is broad, thin, scoop-shaped, reg- 
ularly rounded in front, and notched (v) at the side in front of the nasal 
sac (d). Behind it the broad anterior foramen (/) extends quite to the 
interorbital space. On this space a second foramen (p), open in younger 
specimens, is indicated by a narrow depression or gash, not reaching 
through the cartilage. <A little farther back there is a rounded space in 
which the surface is rugose (0). From the parietal fossa (7) there are 
two pores on each side, as in Heptabranchias. Professor Gegenbaur 
figures four in Hexanchus also, but places them in a transverse series. 
Behind the fossa a low occipital crest extends to the vertebrae. The 
preorbital process (f) is moderately stout ; its outer end is unseg- 
mented and rests close upon the pterygo-quadrate at its outer edge. 
Above the eyes the expansions are thin and prominent. Of the supra- 
orbital foramina (2) the anterior is the opening for the ramus ophthal- 
micus and in front of the latter is the upper opening of the ethmoidal 
or preorbital canal (e). The postorbital process is of irregular shape and 
moderate breadth. There are three lateral processes on the occipital 
region. The first is seen in the paroccipital region. The second (¢) is 
