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TRANSACTIONS OF THE AMERICAN PHILOSOPHICAL SOCIETY 



After a careful consideration of these opposing evidences and interpretations, I can 

 only record my impression that the older view is by far the more probable, and that for 

 many reasons, only a few of which may here be noticed. 



.na 

 3ub.ord 



■sup orb 

 dsph 



Scaphirhynchus platorhynchus 



Fig. is. Scaphirhynchus platorhynchus. Courtesy of Dr. E. W. Gudger. 



Whatever may be said as to the sturgeon, it can hardly be doubted that the exoskeleton 

 of the spoonbill {Polyodon) is in a highly retrogressive condition. In place of the fully 

 formed ganoid scales of its palaeozoic relatives it has a practically naked body with a few 

 vestigial horny scales in the upper lobe of its heterocercal fin. Assuredly its so-called 

 opercular plates have the appearance of being degenerate structures and the same is true 

 of the thin derm-bones that overlie its palatoquadrate and Meckel's cartilage. In spite of 

 its degenerations, however, the entire suspensorium is evidently of a modified primitive 

 actinopteran type, differing from the elasmobranch especially in the presence of a large 

 symplectic and of an "opercular" plate. The shoulder-girdle is that of an actinopteran, 

 not that of a progressive shark. In view, therefore, of its degenerative specializations 



