INTRODUCTION. 63 



fishes. No. 1 is the principal frontal bone ; 2. 

 Anterior frontal bone ; 3. Posterior frontal bone ; 

 4. Temporal bone ; 5. Parietal bone ; 6. Maxillary 

 bone ; 7« Intermaxillary bone ; 8. Suborbitary 

 bone; 9. Supra scapular bone; 10. Preopercle ; 

 11. Opercle; 12. Subopercle ; 13. Interopercle. 

 The above references will enable the observer to 

 understand the characters of the genera, which 

 are, in a great measure, taken from the form of 

 these bones in the head. 



In the perch, and indeed in all those fishes which 

 are endowed with extensive locomotive powers, or 

 require swiftness to seize their prey, the tail is 

 the great organ of motion, while the fins are the 

 balancers or directors, a contrary arrangement to 

 that shewn in the members of those creatures of 

 the land and air, where the tail is the director or 

 helm, the feet and wings the movers. The fins on 

 the upper surface serve to balance the body, those 

 on the lower surface to turn it, to move it slowly, 

 and to keep it suspended in strong currents ; but 

 in all these, the motion or assistance of the 

 tail is observable. In very swift motion the fins 

 are quiet; the creature could not keep them 

 extended, far less use them, and they fold closely 

 to the body, and offer no resistance to its rapid 

 passage through the water. In what are called flat 

 fish, however, and in all those whose horizontal 



