8 BULLETIN OF THE 



alone it is doubtful whether close affinities would be suspected. In the 

 Notidanidae 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 majoi'ity 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 embr^^o 

 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, PI. 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 (i) 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 (o). From the parietal fossa («) 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 (/) 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 (h) 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 latei-al processes on the occipital 

 region. The first is seen in the paroccipital region. The second {t) is 



