694 Suborder Heterosomata 
or in any other flounders outside the fauna of northern Cali- 
fornia, Oregon, and Alaska. 
Ancestry of Flounders.— The ancestry of the flounders is 
wholly uncertain. Because, like the codfishes, the flounders 
lack all fin-spines, they have been placed by some authors after 
the Anacanthini, or codfishes, and a common descent has been 
assumed. Some writers declare that the flounder is only a 
codfish with distorted cranium. 
A little study of the osteology of the flounder shows that 
this suppositicn is without foundation. The flounders have 
Fic. 598. 
Fias. 597 and 598.—Larval stages of Platophrys podas, a flounder of the Mediterra- 
nean, showing the migration of the eye. (After Emery.) 
thoracic ventrals, not jugular as in the cod. The tail is homo- 
cercal, ending in a large hypural plate, never isocercal, except 
in degraded soles, in which it is rather leptocercal. The shoulder- 
girdle, with its perforate hypercoracoid, has the normal perch- 
like form. The ventral fins have about six rays, as in the perch, 
although the first ray is never spinous. Pseudobranchie are 
developed, these structures being obsolete in the codfishes. The 
gills and pharyngeals are essentially as in the perch. 
It is fairly certain that the Heterosomata have diverged from 
the early spiny-rayed forms, Zeoidei, Berycoidei, or Scombroidei 
