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TRANSACTIONS OF THE AMERICAN PHILOSOPHICAL SOCIETY 



ticulum, using the greatly elongated supracleithra and postclavicles as levers to work the 

 bellows. The supracleithra, which are quite short and vertically-placed elements in the 

 teuthids and lower plectognaths, then became pulled out into long oblique or nearly hori- 

 zontal rods, which are so conspicuous that they have been used as diagnostic characters for 

 the different families; but that the elongation and sub-horizontality of the supracleithra 

 are quite secondary is indicated not only by their association with the newly-evolved 

 puffing apparatus but also by the parallel elongation and oblique position of the opercular 

 and subopercular and by the pulled-out appearance of the lower corner of the preopercular. 

 This backward prolongation of the subopercular might have caused the disruption 

 of the bony tracker of the interopercular but this important mechanism for tying the 

 opercular series to the jaw was thereupon shifted from its normal contact with the 



ft. 



dilalorfoisa 



iphot 



...pto .. soo 



Diodon sp. 



Diodon hystrix 



Fig. 170. Diodon hyslrix. 



junction of the opercular and the subopercular to a position on a special inner ridge of 

 the opercular (Fig. 1685). 



The backward pulling of the opercular also caused the dorsal process of the opercular 

 to overlap the outer side of the hyomandibular. The same backward dragging movement 

 also shifted the posterior process of the pterotic from its more vertical position in Lactophrys 

 to its backward and downward direction in Spheroides. In brief, all the signs point in- 

 dubitably not only to a shortening of the muzzle but also to a secondary flattening down 

 of the whole head in Lagocephalus, thus producing the horizontality of the parasphenoid 

 and the terminal position of the now enlarged and widened mouth. 



Diodonts. — In the diodonts or porcupine fishes the puffing apparatus is doubtless re- 

 sponsible for the elevation of the pectoral fin, for the sub-horizontality of the supracleithrum, 

 for the backward expansion of the opercular and preopercular. 



