338 PECULIAKITIES OF PLAICE FROM DIFFERENT FISHING GROUNDS. 



on the coast of the United States cliielly, if not exclusively, in winter ; 

 and we may conclude that the low temperature of the water in winter 

 excludes the plaice, while the high summer temperature prevents 

 the extension of glacialis further to the south. 



Pleuronedes ficsus. We have next to consider the flounder, which 

 is distinguished from the other two species most conspicuously by 

 the character of the scales, many of which are more reduced than 

 in the plaice, while others on particular parts of the body have taken 

 on a peculiar development, and have been enlarged into prominent 

 thorny tubercles. These tubercles are most constantly present in a 

 single row along the bases of the dorsal and ventral fins, and are 

 also usually present on the head and about the lateral line, while 

 in certain forms they are developed over nearly the whole of the 

 skin of the upper side. 



The species occurs on the east side of the Atlantic all along the 

 coasts of Europe — from the White Sea on the north to the Black Sea 

 at the extremity of the Mediterranean. At different regions within 

 these limits it exhibits local variations. Duncker examined samples 

 from various parts of the Baltic and from the North Sea. In criti- 

 cising his results we must take into account the fact that the flounder 

 is essentially an estuarine iish, often ascending rivers into fresh water, 

 and only descending to the sea in order to spawn. 



In the Baltic the flounder extends much further than the plaice, and 

 generally exhibits a much greater development of tubercles than on the 

 coasts of the North Sea. Duncker examined samples from Kunigsberg, 

 Greifswald, Niendorf, and Kiel. From Kunigsberg he had 20 males and 

 8 females ; the males from 19-0 cm. to 28-2 cm. in length, the females 

 from 23'3 to 28'2 cm. They were remarkable for their very rough 

 squamation, great height of body, very short heads, and conspicuous 

 red spots, approximating to the coloration of the plaice. There were 

 crowded small tubercles over the whole of the upper side, on the blind 

 side at least along the lateral line, on the abdomen, and on the inter- 

 spinous region. The average height of body was 399 per cent, in the 

 males, 4M per cent, in the females. The length of head was 22*3 per 

 cent., and also less in the males. The number of fln-rays was higher 

 than in other Baltic samples, the mean of the dorsal being 58-1, of the 

 ventral 407. The number of gill-rakers was 11-18. 



The Greifswald sample consisted of 14 males, 15 females; the males 

 in length 105 cm. to 260 cm., the females 15-8 cm. to 34-6 cm. In 

 these the squamation was less rough ; the height of body less, 37"8 per 

 cent, on the average ; the head longer. It seems to me all these differ- 

 ences are sufficiently explained by the greater proportion of younger 

 and smaller specimens. The mean numbers of the dorsal and ventral 



