The Jslatural History of the Frilled Shar}{ 269 



normal thickness. This is readily seen in the accompanying figures [AUis, 1919, PI. I, figs. 

 1 and 2] . . . and it is there also seen that what is actually a portion of the external surface 

 of the head when the mouth is widely opened, becomes enclosed between the lips when the 

 mouth is closed. 



Allis (1919) speaks of "primary" and "secondary" lips in Chlamydoselachus, but his 

 description is too involved for consideration here. The reader is referred to his text 

 (1919, pp. 146-147) for his exact wording. However, if the reader will consult our Figure 

 7, plate II, a reproduction of AlHs's drawing of the head in lateral view, and will contrast 

 this with AUis's view of the wide-open mouth (our Figure 9, plate III), he will see these 

 rudimentary lips represented. In both figures the wrinkles at the angles of the mouth are 

 well shown, as are the dense patches of shagreen around the angle. All these structures 

 we find in our adult specimens. 



The peculiar organization of mouth and jaws above described gives Chlamydoselachus 

 a gape which is enormous for such a remarkably slender-bodied shark. Looking at this 

 fish head-on, one sees practically nothing but the wide-open mouth looking like the 

 entrance to a tunnel. For this, see Carman's figure (our Figure 8, plate III) and AUis's 

 head-on figure (our Figure 9, plate III). Even more striking than either of these is our 

 Figure 10, plate III, made from a photograph of the open mouth of the head from Columbia 

 University, in which the distention is greater than in either of the other figures. 



In both Carman's and AUis's figures, the shape of the mouth is about normal, judg- 

 ing by the shapes which the mouths of our three specimens take when distended. The 

 mouth of the Columbia specimen has been much enlarged laterally. Later, these figures 

 will be referred to for other points. 



BREATHING VALVE 



We have found in the mouths of our preserved specimens of Chlamydoselachus a 

 structure which, at first, we thought had escaped the notice of all previous investigators. 

 There is in the mouth at the apex of the upper jaw, in all five of the fish we have ex- 

 amined, a thin crescentic fold or shelf which we interpret as a breathing-valve. This fold 

 extends to the third and fourth rows of teeth on either side, and projects posteriorly 

 into the front upper part of the mouth. There is quite a recess or pocket between it and 

 the front part ot the roof ot the mouth, which extends forward in our specimens dorsal to 

 the jaw-cartilages and between them and the skin. The shelf or breathing-valve is of 

 course very much contracted in our specimens, which have been thirty years in alcohol. 

 But it may be plainly seen in Figures 11 and 12, plate IV, made from photographs of our 

 specimens. In Figure 1 1 the valve is seen to be posteriorly angled like the head of a broad 

 arrow,^ while in Figure 12 it is more rounded. Both, however, are quite evident. The 

 similar structure in our third specimen, and that in the Columbia head, are shown in 

 Figures 11 to 15, plates IV and V. Similar folds of tissue are found in the mouths of 

 many bony fishes — especially those which breathe with the mouth partly open. 



■* Doctor White's specimen possesses a similarly angled breathing-valve. (See Figure 14, plate IV). 



