286 



SYSTEMATIC ZOOLOGY 





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is readily apparent when we recognize that such divergent types 



as the eel, the sal- 

 mon, and the sea 

 horse all belong 

 here ; but the gen- 

 eral description of 

 the external anat- 

 omy of the Teleos- 

 tomi applies to the 

 Teleostei, except 

 that in place of the 

 type of heterocer- 

 cal tail characteris- 

 tic of the Ganoidei, 

 we find usually a 



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homocercal tail 

 with occasionally a 

 diphy cereal caudal 

 fin or none at all. 

 The body is some- 

 times covered with 

 a naked skin, some- 

 times with bony 

 plates, but usually 

 with o v e r 1 a p- 

 ping scales, which 

 sometimes have a 

 smooth, circular 

 border and are 

 called cycloid 

 scales (Fig. 294). 

 and sometimes 

 have a toothed bor- 

 der and are known 

 as ctenoid scales. 



Internally the 

 principal differ- 

 ence between the 

 Ganoidei and the 



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