172 THE STORY OF FISH LIFE. 



tains several forms of considerable interest. One 

 of the most remarkable of these is the formidable 

 hammer-headed shark and the curious angel or 

 monk-fish, very closely approaching the form of 

 the rays in consequence of its similar habits. 

 These are the two most profoundly modified in 

 external form. The largest member of the sub- 

 order is the Charcharodon, and is at the same 

 time the most dreaded, attaining a length of 

 some forty feet. Teeth of a gigantic species, 

 only recently extinct, are occasionally dredged 

 up between Polynesia and the West Coast of 

 America, some of these teeth being as large as 

 those of a fossil species found in the Crag, and mea- 

 suring five inches in length and four iaches wide 

 at the base. The seven-gilled shark of the genus 

 Nokidanus and the Port Jackson shark (Cestracion) 

 are of great interest, on account of certain very 

 primitive characters of the skeleton and the 

 teeth. These last bear a close resemblance to 

 certain fossil forms. Those of the seven-gilled 

 shark are interesting on account of the fact that 

 they are provided with numerous cusps, giving 

 the free edge of the tooth a saw-like appearance 

 resembling similar teeth found in the Eed Crag 

 of Suffolk, and as far back in time as the Jurassic 

 period. Whole skeletons of Notidanus occur in 

 the Solenlufen slates of Bavaria, The Port 

 Jackson shark of to-day, occurring from Australia 

 to Japan, the Galapagos Islands and California, 

 carries us back into the remote past to the 

 Carboniferous period ; teeth differing but little 

 from those of the living Cestracion occurring in 

 the rocks of this age. These teeth it will be 



