Suborder Heterosomata 695 
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 Stromateide, 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 Amplhistium 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. 599.—Platophrys lunatus (Linneus), the Peacock Flounder. 
Family Pleuronectide. Cuba. (From nature by Mrs. H. C. Nash.) 
founders 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 
Anacanthint. 
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: Pleuronectide.—In the flounders, or Pleuronec- 
tide, the membrane-bones of the head are distinct, the eyes large 
and well separated, the mouth not greatly contracted, and the jaws 
