A SYSTEMATIC MONOGRAPH 



FLATFISHES (HETEROSOMATA) 



A. GENERAL PART. 



I. ORIGIN AND SYSTEMATIC POSITION OF THE HETEROSOMATA. 



In the ' Systema Naturae ' of Linnaeus all the Flatfishes known to him were placed 

 in a single genus, Pleuronectes, and it was not until the publication of Cuvier's ' Le Regne 

 Animal ' that any real attempt was made to indicate the relationships of the various 

 groups of Bony Fishes. In Cuvier's (1817)' classification the Flatfishes are raised 

 to the rank of a family, and are associated with the Gadoids, Gobiescocids, Cyclopterids, 

 Echeneids and Ophiocephalids in the division of sub-brachial malacoptery-gians, 

 characterised by the thoracic position of the pelvic fins and the absence of spines in 

 the dorsal fin. Johannes Miiller (1846), who first made use of the relation between 

 air-bladder and gullet for the definition of higher divisions, removed the sub-brachial 

 malacopterygians from the abdominales or physostomes, placing them nearer to the 

 acanthopterygians. In his classification, however, the Pleuronectoids and Gadoids 

 are still associated, a new order, Anacanthini, being erected to include these fishes 

 as well as the Ophidioids. This association of the Flatfishes with the Gadoids was 

 retained in many subsequent classifications, and, indeed, is to be found in a number 

 of modern text-books. Thus, Giinther (1880) divided the order Anacanthini into two 

 main divisions — Anacanthini Pleuronectoidei and Anacanthini Gadoidei. Cope (1871) 

 appears to have been the first to recognise the Flatfishes as a distinct order, to which 

 he applied the name Heterosomata, originally mvented by Dumeril, but he also 

 regarded them as related to the Cods. Gill (1893) regarded the Heterosomata as a 

 suborder of his Teleocephah, equal in rank to the Anacanthini, close to which it was 

 placed. Jordan and his collaborators recognised the Heterosomata as a suborder 

 of the order Acanthopteri, in which it was placed near the Ribbon-fishes (Taeniosomi) 

 and the Cods (Anacanthini). In discussing the systematic position of the Hetero- 

 somata, Jordan and Evermann (1898, p. 2602) state : " Its near relationship is 

 probably with the Gadidae, although the developed pseudobranchiae and the thoracic 

 ventral fins indicate an early differentiation from the anacanthine fishes ". 



Among other views as to the relationships of the Flatfishes, mention may be made 

 of Gill's (1887, p. 86) tentative suggestion that " the Heterosomatous fishes may have 

 branched off from the original stock, or progenitors of the Taeniosomous fishes ", an 



^ See list of references, p. 52. 



