THE FLAT-FISHES 



215 



while in the fourth they are on the left. The develop- 

 ment of teeth in either jaw represents, however, a more 

 satisfactory character. In the plaice, dab, and flounder, 

 representing the first group, there is unequal development 

 in two sides of the jaws. In the halibut, representing the 

 second, the teeth are equally developed in both sides. In the 

 sole, representing the third, there are teeth on one side only. 



The fact that the so-called upper and lower surface of 

 flat-fish are in reality the right and left side is at once 

 made apparent by the presence of the lateral line along each. 

 The terms " right " and " left," by the way, are used in 

 respect of an observer holding the edge with the mouth 

 and vent towards him. The dorsal fin runs along the edge 

 farthest from the mouth ; the ventral fin is long ; and the 

 vent lies close to the head. 



As in the case of the cod family, one or two rarer kinds 

 of the present group have been briefly noticed in Chapter 

 XIV. Those described in the present chapter are as 

 follow : — 



Sub-Order : HETEROSOMATA 



