The ?<[atnral History of the Frilled Shar\ 279 



NOSTRILS OF THE FRILLED SHARK 



The nostrils, placed near the front of the snout, open on a surface that faces anteriorly, 

 ventrally, and laterally, which is about the most favorable location imaginable for an organ 

 whose function depends on a rapid intake and egress of water. Garman figures the 

 nostrils (our Figure 8, plate III; and Figure 16, plate V) and describes them (1885.1, p. 2) 

 as follows: 



Each nostril is vertically elongate, and so constructed that the upper half opens forward 

 and the lower half backward. 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 opening but not the chamber; it is formed by a sharp fold push' 

 ing backward 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 covering the nostril. 



These figures and this description fit our specimens fairly well. Our fish are too 

 distorted by being coiled up in barrels and by the action of preservatives to permit good 

 drawings of the nostrils to be made. We think these organs are admirably shown in AUis's 

 drawing — Figure 9, plate III. 



SPIRACLES OF CHLAMTDOSELACHUS 



The spiracles, which are typical elasmobranch respiratory organs representing a 

 modified anterior pair of gill'slits, are present though almost vestigial. Each spiracle lies 

 near the top of the head at the middle of a line joining the upper surface of the eye with the 

 medial dorsal edge of the first gill'fold. 



Our largest fish has had the top of the head much bruised and cut, especially on the 

 left side, where we can find no trace of the spiracle. On the right side we find an aperture, 

 2 mm. in diameter, which we believe to be the spiracle. In our second largest specimen 

 (1485 mm.), the spiracles are about the same size as in the former. The head of our smallest 

 fish (1350 mm.) shows the spiracles most clearly, although they are somewhat smaller. In 

 the well'preserved head from Columbia University they are definite oval slits about 3 mm. 

 in length. Through one of these we inserted a bristle which came out into the pharynx 

 through a fairly large opening (large enough to admit the blunt end of a pencil) in series 

 with the other branchial clefts and situated in front of the hyomandibular. In our 304'mm. 

 embryo the spiracles are visible under a reading glass, but cannot be identified with the 

 naked eye. Of these organs, Garman remarks (1884.2, p. 116) as follows: "The spiracles 

 are so small as to be almost useless; but, being present, they point toward an ancestor, a 

 bottom'feeder, in which they were more developed." 



The position of the spiracle (according to our specimens) is correctly shown by 

 Garman in our Text'figure 7, and by AUis in our Text'figure 21. But it is placed entirely 

 too far back in Collett's plate (our Figure 6, plate II). Either there is great variation in 

 the position of the spiracles, or the artist has taken great Hberties with his subject. 



