Suborder Heterosomata 485 



of the Jurassic or Cretaceous, and that their origin is prior to 

 the development of the great perch stock. 



If one were to guess at the nearest relationships of the group, 

 it would be to regard them as allies of the deep-bodied mackerel- 

 like forms, as the Stromateida, or perhaps with extinct Berycoid 

 forms, as Platycormus, having the ventral fins wider than in the 

 mackerel. Still more plausible is the recent suggestion of Dr. 

 Boulenger that the extinct genus Amphistium resembles the primi- 

 tive flounder. But there is little direct proof of such relation, 

 and the resemblance of larval flounders to the ribbon-fishes may 

 have equal significance. But the ribbon-fishes themselves may 

 be degenerate Scombroids. In any case both ribbon-fishes and 



FIG. 43l.Platophrys lunatus (Linnaeus), the Peacock Flounder. 

 Family Pleuronectidce. Cuba. (From nature by Mrs. H. C. Nash.) 



flounders find their nearest living relatives among the Bery- 

 coidei or Zeoidei, and have no affinity whatever with the 

 isocercal codfish or with other members of the group called 

 Anacanthini. 



The Heterosomata are found in all seas, always close to the 

 bottom and swimming with a swift, undulatory motion. They 

 are usually placed in a single family, but the degraded types 

 known as soles may be regarded as forming a second family. 



The Flounders : Pleuronectidae. In the flounders, or Pleuronec- 

 tida, the membrane-bones of the head are distinct, the eyes large 

 and well separated, the mouth not greatly contracted, and the jaws 



