4S FLATFISHES (HETEKOSOMATA) 



siuh (actors as ti-miicratiirc, salinity, etc Hubbs (1922, 1924. 1925, 1026) has more 

 recently i)nblishe(l a series of iniinutant imjhts ikaluiR with this matter, and concludes 

 that " the addition of somites. \\ \)u li is pi.M in ilU synonymous with the growth of the 

 embr\'o. proceeds faster under aci 1 li ratiiii; than under retarding conditions of develop- 

 ment, but terminates relatively sooner and more abruptly. As a consequence, warm 

 or brackish water forms of a fish have as a general rule fewer vertebra; than the forms 

 inhabiting cooler or more saline water." There can be little doubt that a statistical 

 .study of large numbers of specimens of a species of Flatfish would reveal the existence, 

 m some species at least, of a number of well-marked races, distinguished mainly by 

 numerical characters similar to those mentioned above. Duncker has shown that 

 the I'laice of the Baltic difters from that of the North Sea in having an average of one 

 \ertcbra less, five rays less in both dorsal and anal fins, and one more ray in the 

 pectoral fin (see p. 354). 



\"III. (iEOGKAl'HICAL DISTKim'TIO.X. 



The gcnercd distribution of the families and subfamilies of Heterosomata included 

 ill the present volume is summarised below, the latitudinal range being indicated in 

 the accompanying diagram (Fig. 29). 



I . Psellodidtr. 

 Includes a single genus, with one species from tropical West Africa and another 

 from the Indo-Pacific. 



2. Bolhida-. 



(a) Paraluhthina-. — Widely distributed in tropical and temperate seas. Eleven 

 genera are represented on the Atlantic coast of North and South America, and the 

 same number on the Pacific coast ; of these, eight genera are represented by species 

 on both coasts. On the Atlantic coast the subfamily ranges from the region of Cape 

 Cod to the Magellan-Falkland Islands plateau, and on the Pacific coast from British 

 Columbia to Chile. The genera Syacium and Citharichthys, from both coasts of 

 America, are also represented on the coast of West Africa, in the case of Syacium by 

 the .same species [micrnruni) as that of the western Atlantic, and in the case of Citha- 

 richthys by a species very closely related to one from the Atlantic coast of tropical 

 America. Species of Paralichthxs occur on both sides of America, and there is one 

 species in China and Japan. The single species of Eucitharus is found in the Mediter- 

 ranean and on the West African coast. Citharoidcs is represented by a single species 

 from the Cape and from Japan, There are no representatives of this subfamily on 

 the coasts of north-western Europe. There are six genera in the Indo-Pacific. where 

 the subfamily ranges from the Red Sea and the east coast of Africa eastwards through 

 the Indian CJcean and Archipelago to the Pacific. In the Pacific it appears to extend 

 its range northwards to about latitude 45° N., and .southwards to about latitude 35° S. 



(b) Bolhinrr. — Also widelv distributed in tropical and temperate seas. On the 

 .\tlantic coast of America it is represented by the genus Bothiis, which ranges from 

 Long Island to Rio de Janeiro, and by Mancopselta andAchiropsetta from the Magellan- 

 Falkland Islands plateau. The same species of Mancopsetta is also found near Prince 

 Ed\vard's Island in the southern part of the Indian Ocean. On the Pacific coast of 

 America species of Bolhus again occur, and this genus is also represented on the eastern 

 side of the Atlantic as well as in the Mediterranean. There are no species common 

 to the two sides of the Atlantic, but Bothus ocellaiiis of the Atlantic coast of tropical 

 America is closely related to B. mellissi of St. Helena and Ascension, and to B. podas 

 of the Mediterranean and west coast of Africa, etc. On the eastern side of the Atlantic 

 the subfamily ranges considerably farther north than the Paralichthinae, extending 

 ns far as northern Scotland, the Cattegat and Christianiafiord. Arnoglossus is a widely 

 distributed genus, being found on the coasts of north-western Europe and in the 



