330 TECULIARITIKS OF rL.VICE FItOM DIFFERENT FISHING CxROUNDS. 



characters more to those of the North Sea, although it might be 

 expected that, the locality being farther inwards in the Baltic, they 

 would be more different from the plaice of the North Sea. I fail, 

 however, to find in Duncker's description any dilferences to which 

 such importance can be attributed, especially when the small number of 

 specimens is considered. The four males are all small and youn^, 19'6 

 to 22G cm., and this would partly account for the slightly lower height 

 of body and greater length of head which Duncker mentions. The 

 number of gill-rakers reaches 13, but I fail to see any difference in the 

 number of fin-rays. The degree of ciliation was 2 in all four male 

 specimens, which is in accordance with their small size. 



We see then that as far as the small amount of evidence at our 

 disposal goes, the Baltic plaice are modified in the same direction 

 as northern forms in the North Sea with regard to reduction of fin- 

 rays and increase of spinulation, and to a much greater degree, wliile 

 with regard to other characters, branchial rays, height of body and 

 length of head, no very distinct differences are exhibited. In accordance 

 witli the reduction of the dorsal and ventral fins, the caudal peduncle 

 is a little longer in the Baltic. It is interesting to notice that as we 

 proceed northwards in the North Sea and Atlantic these modifications 

 are associated with a great increase in total size, while in the Baltic 

 there is an equally conspicuous decrease in size. This proves that 

 the modifications are independent of the rate of growth, and therefore 

 presumably of the amount of available food. 



III. The Eelatioxs between Local Variations and Specific 

 Characteus in the Plaice and Allied Species. 



The plaice and flounder are certainly very closely allied, and there 

 is a third form which also differs but slightly from them. This third 

 form is the Pleuronedes glacialis of Pallas. To study the relations 

 of these three forms to one another we must take a general survey 

 of all that is known concerning their whole distribution, and their 

 variations in different parts of their habitats. The question has 

 previously been discussed by Professor Smitt in his edition of the 

 Scandinavian Fishes of Fries and Ekstnim, 1893, and by Duncker 

 in the paper frequently cited above; but I have endeavoured, by 

 examining additional evidence, to carry the investigation somewhat 

 further. 



Pleuronedes platessa. Southwards on the European coast the plaice 

 seems to extend into the Mediterranean, although I liave not been 

 able to discover any very definite or detailed account of specimens 

 from that sea. Smitt mentions its existence there, and Jordan and 



