2 BULLETIN OF THE 
The gape is wide. The structure of the mouth and throat is such as 
to permit the creature to swallow with ease others whose bodies have 
diameters as great as its own, or even greater. Both mouth and throat 
are lined with shagreen. On the inner edges of the gill arches the scales 
are larger. At the angles of the jaws there are neither labial folds nor 
labial cartilages. i 
The eye is moderately large ; it is on the side of the head, over the 
middle of the length of the mouth, and, from the sharp rather prominent 
brow, has a savage look. The pupil is horizontally oblong. Around the 
pupil the skin covering the eyeball is rough with small scales. There 1s 
no trace of a nictitating membrane. 
The slightness of the convexity of the top of the head makes the angle 
formed with the sides, in front of the eyes and around the snout, some- 
what sharp. The snout extends but little in advance of the mouth. 
The nostrils are lateral; they are placed about half-way from the 
eyes to the end of the snout. Each nostril is vertically elongate, and so 
constructed that the upper half opens forward and the lower half back- 
ward. Internally the nasal chamber is not divided. During forward 
motion the water enters through the upper section of the nostril, passes 
downward behind the partition and out again through the lower section. 
Backward motion reverses the current. The partition divides the open- 
ing, but not the chamber; it is formed by a sharp fold pushing back- 
ward from the middle of the front wall to meet a similar fold from the 
opposite side. In the Notidanide the structure is similar. Commonly 
among Selachians the anterior fold takes the form of a flap partially coy- 
ering the nostril. 
The gill-openings are large; the first, when extended, will admit an 
object of four inches or more, and the last will take one of two inches in 
width. A vertical from the upper angle of the fifth touches the front 
edge of the pectoral, and a third part of the sixth opening passes back 
above the same fin. The arches are quite slender. ‘The blade-like folds 
of the membrane are free for a considerable extent of their length at the 
outer end. Plate V. gives the appearance in the fourth opening on the 
right side. Sharp points on the edges of the gill-covers indicate the 
ends of the branchial rays. The opercular flap, or first gill-cover, is 
broad and free around the neck, except for a short space behind the 
occiput. A thin inner fold descending from a point in front of and be- 
neath the first branchial cartilage connects the flap with the isthmus. 
As is to be expected in connection with large branchial apertures, the 
spiracles are very small. 
