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. 



The eye is moderately large ; it is on the side of the head, over the 

 middle of the length of the moiith, 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 is 

 no trace of a nictitating membrane. 



The slightncss 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 Notidanidae the structure is similar. Commonly 

 among Selachians the anterior fold takes the form of a flap partially cov- 

 ering the nostril. 



The gill-openings are large ; the fii'st, 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-cnver, 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 copnects the flap with the isthmus. 



As is to be expected in connection with large branchial apertures, the 

 S2:)iracles are very small. 



