The Jiatural History of the Frilled Shar}{ 275 



the breathing-valve, a transverse row of minute denticles across the hinder base of the 

 symphysis. These are in pairs, but at the right of the line three are found which look like 

 a tri'cusped tooth. Between the second and third rows of teeth in this right upper jaw, 

 far back toward the ''gum" behind the teeth is what appears to be a very small three- 

 cusped tooth. All these spinose structures we interpret as imperfectly developed teeth. 

 A row of four single-cusped teeth, very similar to those shown in Figure 15, plate V, is 

 found in the upper jaw of Doctor White's specimen immediately anterior to the V-shaped 

 breathing- valve. All this is excellent evidence supporting the commonly accepted belief 

 that the teeth of a shark are strongly metamorphosed dermal denticles. 



In this connection we have carefully examined the six embryos in our possession 

 (ranging in length from 190 mm. to 374 mm.). These all have tooth-pads through which 

 the teeth have not yet broken, but not one of them has such a pad in the middle of the 

 upper jaw. Each one does have such a central pad at the point of the lower jaw — how- 

 ever, in one fish only this pad is sHghtly twisted to the left. So slight is this that the 

 twisting is possibly due to displacement while the specimen was being hardened in formalin. 



In our four adult specimens and in the head from Columbia University, we find the 

 ventral surface of the breathing-valve covered with shagreen as may be seen in Figure 13, 

 plate IV, and in Figure 15, plate V. Moreover the folds of tissue which form the "gum" 

 behind the teeth, and also the tongue and in general the lining of the mouth, are covered 

 with shagreen in some cases closely simulating teeth. 



Authors report varying numbers of teeth in the various rows. These enumerations 

 are exceedingly difficult to make, but we have accurate counts for three sets of jaws 

 in which we were able to distinguish the teeth in every row. For a fourth (our fish No. 

 II), we were able to get the count in the lower jaw only, the last rows of both sides of the 

 upper jaw having the small teeth and the adjoining tissues so torn and mangled (possibly 

 when caught on a hook) that no accurate count could be made (only 95 teeth could be 

 recognized). Our results are set in order in Table IX. 



When one studies Table IX, where the rows are analyzed to show the number of 

 teeth to a row, one must conclude that in the matter of the teeth, both in the number of 

 rows and in the number of teeth in each row, Chlaynydoselachus is in a plastic condition. 



It is significant that, unUke what is found in almost all other sharks, practically all 

 the visible brier-like teeth in every row in the mouth of Chlamydoselachus are functional 

 at once, hence a large number are usable and are used. For this see all the figures of the 

 open mouth. In our specimen No. I there are 140 teeth in the upper jaw and 134 in the 

 lower, 133 on the right and 135 on the left plus 6 in the center; a total of 274 for the mouth. 

 The table and its footnotes explain why complete figures cannot be given for fish No. II. 

 In the jaws of No. Ill, there are 122 teeth in the upper jaw and 128 in the lower. These 

 are also thus divided: 122 on the right side, 122 on the left, with 6 in the center; and the 

 totals are 250 in each count — upper-lower and right-left. In the Columbia University 

 specimen we find 144 teeth above and 118 below, total 262. These are divided as follows : 

 122 on the right, 122 on the left, plus 18 in the center — a total of 262. 



