88 



PRIMITIVE LIVING SHARKS 



Recent Sharks -z 



The forms of Sharks and Rays 

 common at the present time are 

 generally looked upon as closely % 

 related genetically, although 

 their lineage cannot be defi- 

 nitely traced. As far as palse- 

 ontological evidence goes, they 

 may well have been derived 

 from a single Palaeozoic an- 

 cestor. 



Perhaps of all recent forms, 

 ChlamydoselacJic (Fig. 92), and 

 Notidanus (Heptanchus, or Hep- 

 tabranchias) (Fig. 93), which are 

 universally regarded as "primi- 

 tive," have inherited most di- 

 rectly the features of this gen- 

 eralized Palaeozoic form. But 

 which of these two sharks must 

 be regarded as resembling its re- 

 mote ancestor the more closely 

 seems to the writer a very doubt- 

 ful matter. Chlamydoselache 

 derives its great interest from 

 its late discovery (1884, Gar- 

 man), rareness, and Pleuracan- 

 thid type of teeth (Fig. 92, A) ; 

 but now that it has been taken 

 in numbers — comparatively — 

 in deep water, one is inclined 

 to believe that many of its 



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