54 AN EXTRAORDINARY SHARK; 



from the structure and apparent age of the specimen, to be 

 probable. The delicate margins and filaments of the fins 

 are those of an inhabitant of the open sea or considerable 

 depths. Bottom feeders are provided with larger spiracles 

 and the fins usually show signs of wear. Rapidity of 

 movement is suggested by the large amount of surface in 

 the posterior fins. It is probable, however, that the large 

 fins, being so far back, are of importance as support for the 

 body when the anterior portion is quickly plunged forward 

 to seize the prey ; that is, they secure a fulcrum from 

 which the animal may strike like a snake. The anterior 

 fins (pectorals) being only of moderate size are yet ample 

 for balancing or directing the body when in motion how- 

 ever rapid. 



There is a correspondence between the size of the gill 

 openings and that of the mouth ; no matter how widely 

 the latter may be opened when rushing upon the prey, 

 the immense branchial apertures allow the water to pass 

 through without obstruction. Favoring the idea of rapidity 

 of movement still further are the peculiarities in the struc- 

 ture of the nostrils. By means of a fold from each side 

 of the vertically elongated nostril it is divided into what 

 appears to be two nasal apertures. Of these the upper looks 

 forward and catches the water as it is met turning it into 

 the cavity upon the membranes of the interior ; while the 

 lower opens backward allowing the water to escape after 

 passing over the olfactory apparatus. In case of the 

 upper opening it is the hinder margin that stands out 

 farthest from the head and in the lower aperture it is the 

 forward edge that is prominent. In fact the structure is 

 such that 'the slightest forward movement will send a cur- 

 rent of water in at the upper portion of the nostril and out 

 at the lower while a move backward will simply reverse 



