THE BRAZILIAN PERCOPHIS. 263 



The third series of scales are named Ctenoid, or comb-like scales, on account of the 

 toothed projections in their posterior edge. The beautiful scales of the Perch, so 

 largely used in the manufacture of feminine ornaments, are familiar examples of cte- 

 noid scales. The last class are the Cycloid, or rounded scales without teeth, such as 

 those of the carp. 



On careful examination, the scales are found to be composed of two layers, which 

 can be separated by careful manipulation, and their structure is permeated with chan- 

 nels, either partially closed so as to form grooves, wholly so, and then become tubes. 

 The comparatively straight lines which radiate towards the circumference, and the 

 wavy lines which are drawn concentrically and cover almost the entire scale, can be 

 referred to a common spot, called technically the " focus." This spot cannot rightly be 

 termed the centre, because it is of variable dimensions, and, moreover, is seldom if 

 ever placed exactly in the middle of the scale. 



BRAZILIAN PERCOPHIS.-Percop/i/s Braziliaaus. 



Many scales throw out strong tooth-fike projections, which in point of fact are the 

 teeth of the external skin, and in some species, such as several of the dog-fish, are of 

 crystalline hardness. In some fish, such as the stickleback, a few of these processes 

 of the skin are developed into long sword-like weapons ; in others, such as the trunk- 

 fish, they are fused together, and form a continuous bony envelope to the body, pierced 

 for the protrusion of the tail and fins ; in some, of which the diodons are good ex- 

 amples, they cover the body with an array of projecting spikes, like the quills of the hedge- 

 hog or porcupine, and in others, such as the sturgeons, are arranged in rows of bony 

 plates along the body. 



WE return to the species now under consideration. 



The BRAZILIAN PERCOPHIS is found upon the coasts of Brazil, and is apparently the 

 sole representative of the genus in which it has been placed. The first dorsal fin is 

 very small in proportion to the second, and the space between them is about equal to 

 the length of the first dorsal. The ventral fins are set very far forward, being placed 

 under the throat. The lower jaw projects considerably beyond the upper, and the cleft 



