VERTEBRATA 



FlG. 224. Green sunfish on her nest. Photograph one fifth natural size. 



The flatfishes or flounders are valuable food fish of the sea. 

 The halibut is the largest, weighing four hundred pounds, 

 but the flounder (Pleuronectes americanus) is most fre- 

 quently seen in market. It is remarkable for having two 

 eyes on one side of the head and none on the other. It 

 swims on the side, the lower surface, which is white, always 

 remaining in that position. The young are symmetrical, 

 having an eye on either side of the head and swimming 

 upright. 



Lungfishes (Dipnoi). In this order only three species 

 are included. They live in Australia, Africa, and South 



