The Isiatural History of the Frilled Shar\ 



271 



found his line of reasoning rather difficult to follow and have thought it best to quote him 

 quite fully. He gives no figures of this breathing'valve. 



Our conception of the action of this breathing'valve is as follows: when the creature 

 is resting quietly on the bottom, with the mouth sUghtly open, the breathing-valve doubt' 

 less helps to prevent the regurgitation of water during the process of expulsion of the 

 water through the wide'Open gill'sUts. 



TEETH OF CHLAMTDOSELACHUS 



The fang'like teeth are arranged in rows extending obliquely from front to back across 

 each jaw, as may be seen in Figures 8,9, and 10, plate III; also in Figures 11—14, plate 

 IV; and lastly in Figure 15, plate V. A single row of teeth, about 1.8 times the natural 

 si2;e, is portrayed in both dorsal and ventral aspects in Text'figure 9. These are enlarge- 

 ments of the teeth found in Giinther's drawing (Figure 1, plate I). They have been 

 retouched by our artist to make them sharp and 

 clear'cut. The single teeth have been enlarged 

 about 3.4 times. 



The rows are separated by toothless spaces, 

 which are in width about equal to the width of 

 the adjacent rows of teeth. Posteriorly the spaces 

 become narrower, and at about the seventh or 

 eighth row of teeth, the toothless spaces become 

 very much reduced and the rows of teeth are so 

 closely set that it is difficult to distinguish the 

 rows. The teeth in these posterior rows are very 

 small and are rudimentary in structure. In the 

 symphysis of the lower jaw there is a median row 

 of teeth. At the point of each jaw the outermost 

 teeth of each row are bent so far out beyond the 

 margin of the jaw that they are on the exterior 

 when the mouth is closed. This is particularly 

 true of the lower jaw. For all these points see 

 Plate III, figures 8, 9 and 10. 



In their form the teeth are unlike those found 

 in any other existing shark. Each tooth has three 

 slender, curved, inwardly directed cusps or den- 

 ticles set on a broad base (Text-figure 10) which 

 projects behind and interlocks with the base of 

 the tooth posterior to it, so that it cannot ordinarily be overturned by an outward pull. 

 There are a central and two lateral cusps of approximately the same sizje, and between 

 the central and each lateral cusp is a rudimentary cusp or denticle. For these details of the 

 structure of the teeth of Chlamydoselachus see our Text-figure 10 where a tooth is drawn 



Text-figure 9 

 The teeth of Chlamydoselachus in rows: A, 

 from above and in front; B, from below. 

 Note how the base of each tooth is anchored 

 underneath the base of the tooth behind it, to 

 resist a pull tending to tear it out. The single 

 teeth are X about 3.4, the tooth rows X 

 about 1.8. 

 After Gunther, 1887. 





3RAK 





