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INTRODUCTION. 



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IV. 

 DIPNOI. 



SiRENOIDEI. 



[Unknown.] 

 Artiirodira. 



III. 

 HOLOCEPHALI. 



[Unknown.] 

 Chijleroidei. 



[Unknown.] 



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II. 

 TELEOSTOMI. 



Crossopterygii. 

 (Palseoz. and Mesoz.) 



Crossopterygii. 

 (Cainozoic.) 



ACTINOPTERYGII. 



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iciitiiyotomi. 

 Selaciiii. 



acantiiodii. 



Stages in 

 Evolution of 

 Paired Fins. 



1. Archipterygium 

 (elongate or abbre- 

 viate). 



2. Pectorals di- or tri- 

 basal ; pelvics abbre- 

 viate. 



3. Basal cartilages 

 small or rudimen- 

 tary. 





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