EDIBLE FISHES OF QUEENSLAND.— OGILBY. 133 



the flat-fishes is wholly due, that of the blind side being much the broader, while 

 the frontal of the eyed side is displaced outwards and doAvnwards to form an 

 interorbital bar, the main portion of which is on the wrong side of the eye. 



For a long time it was considered that the movement of the eye resulted 

 in a torsion of the orbital region of the skull, but modern embryological research 

 does not bear out this view. Rather it appears that of the two cartilaginous 

 supraorbital bars, which in the larva are the precursors of the frontal bones 

 of the adult fish, that part, which lies in the path of the migrating eye, is 

 rapidly absorbed, and thus reduced to a pair of processes, directed respectively 

 forward and backward, between which the eye passes and, in assuming its final 

 position, causes a torsion of the supraorbital bar of the future eyed side, which 

 also affects the ethmoid region, ossification not taking place until the migration 

 is complete. 



Recent research into the modifications of the orbital and nasal regions 

 of the cranium, and the composition of the fin-rays in these fishes, tends to prove 

 that the Heterosomata, instead of being asymmetrical gadoids, as was held by 

 earlier writers, have a closer affinity to the percoid fishes. Psettodcs, in fact, with 

 its spinous fin-rays to the dorsal and ventrals, and the more or less vertical 

 position assumed by the body when the fish is moving rapidly, is merely an 

 asymmetrical percoid. In other genera some of the dorsal, anal, and ventral 

 raj's are simple, and plainly represent spines reconverted to articulated rays. 



Geologically the heterosomes date back only to the Upper Eocene, and are, 

 therefore, a but recently differentiated group. Species inseparable from the 

 existing genera Bothus and Solea have been discovered in that formation, but 

 with these exceptions heterosome remains are few, fragmentary, and inconclusive. 

 According to Regan the extinct AmpMstiidce of the same geological age are 

 percoids, with affinities to the recent genus Psettus (Diamond Fishes), or perhaps 

 to Platax — near which it is arranged by Woodward^ — and hypothetically are the 

 symmetrical prototypes of the flat-fishes. Up to the present time but one species 

 — Amphistiuiii parado:niin Agassiz^ — has been discovered ; it is associated by 

 Boulenger^ with the Zeidm (Dories). 



Geographically the Order is practically cosmopolitan, being found in 

 greater or less abundance wherever fisheries can be maintained, and though, as 

 might be conjectured, it is richer in genera and species in the warmer seas, it is 

 to the colder waters of the North Temperate Zone that we must turn, in order to 

 find them in the full zenith of their power and influence. 



Their bathymetrical distribution is also very great, for though the 

 majority of flat-fishes lead a wholly marine life, many species prefer the muddy 

 waters of estuaries to the purity of the open bay, and a few degenerates, 

 chiefly of the soleiform group, elect to pass their entire existence in fresh water, 

 A large number are denizens of the litoral zone, and, as they take a bait greedily 

 and fearlessly, have thereby endeared themselves to the heart of the juvenile 

 angler the world over. But a large and important section — those which enter 

 into the economic food supply of mankind — is taken by the trawl-net, the boulter, 

 and the hand-line, at greater depths offshore, even up to 300 fathoms, at which 

 depth the halibut fishery of the Banks of Newfoundland is lucratively prosecuted. 



1 Brit. Mus. Catal. Foss. Fish., iv, 1901, p. 434. 



2 Poiss. Foss., V, pt. i, p. 44, pi. xiii. 



3 Cambridge Nat. Hist., vii, 1904, p. 684, fig. 417. 



