88 THE BANDED OPHISURUS. 



rapid progression for a length of time, is a lunated, 

 or crescent form, having the breadth and depth of 

 the curvature in certain relative proportions : that 

 which we see in the common trout and the salmon ; 

 that of the pilot-fishes is also near this proportion. 

 These fishes have the power of very rapid and long 

 sustained motion in the water, and immense power, 

 as we shall afterwards see, of surmounting obstacles 

 in their courses. The migrations of the salmon, 

 and its ascending rivers filled with rapids and water- 

 falls is familiarly known ; while the power of 

 swift and long-sustained motion will be exemplified 

 in the genus Naucrates, or pilot-fishes. In both of 

 which, we see this powerful form of tail combined 

 with the tapering, yet solid, construction of the 

 body, and which altogether combines those pro- 

 perties in their highest developement. To illustrate 

 this, we have added a figure of the 



