226 Fart III. — Eighteenth Annual Report 



* Table VIII. 



Region. 



Plymouth. 



Brown Ridges. 



Norfolk Coast. 



N.E. of Dogger 

 Bank. 



No. of speci- 

 mens . 



36 



109 



140 



43 



Dorsal fin 



72-94 



72-98 



73-028 



72-95 



Anal fin . 



54-50 



54-05 



54-27 



54-44 



It will be seen that the averages for the dorsal fin are practically indenti- 

 cal in all — the greatest difference being -088. In the anal fin the 

 difference is larger, being *45 between Plymouth and Brown Ridges. 

 But these two regions are taken together by Cunningham to represent the 

 southern samples, and Norfolk Coast and N.E. of the Doggar Bank are 

 combined to represent a northern group. The averages for these two 

 groups are 54*16 for the southern group and 54 - 31 for the northern. If 

 one could form any conclusion, therefore, from the small difference between 

 these averages it would be that the southern group had a smaller average- 

 number of anal fin-rays than the northern, which is exactly the reverse 

 conclusion to that reached by Cunningham by general reasoning. 



Turning to the Tables IX. and X., it will be seen that the conclusions 

 reached with regard to the vertebrae hold good also for the dorsal and 

 anal fin- rays. The North Sea groups cannot very well be separated from 

 one another, although the group from Helder shows signs that it may be 

 separate. The differences, however, are too fine, as the fluctuations of 

 the averages show, to admit of a definite probability being stated from 

 the characters as to the actual existence of these differences. It can only 

 be said that the plaice from the northerly parts of the North Sea — i.e., 

 Aberdeen — show a tendency to have more fin-rays than those from the 

 southerly parts. The plaice from the Kattegatt come under the same 

 category as those from Aberdeen. 



The plaice from the Sol way Firth, again, show slightly smaller averages 

 than those from the North Sea, but the differences are again too small to 

 admit of any great probability that they would constantly be found were 

 more specimens examined. For the Baltic specimens, however, the case 

 is very different. The fluctuations of the averages show no tendency to 

 overlap, and the probability that these differences are really permanent 

 becomes a certainty when the figures given by Duncker are considered. 

 He found the average for the dorsal fin to be 6 7 -6 and for the anal 50*4, 

 both of which lie within the fluctuations of the averages given here. 



*Made np from numbers given in Jour. Mar. Biol. Ass., Vol., IV., 1897, pp. 356-357. 



f I am obliged to Dr. Duncker of Hamburg for being able to give these values of the 

 Kattegat and a number of the Baltic plaice here. In his paper (I.e.) the values were 

 given as symbols, but he has very kindly permitted me to bring them into line with 

 the system used in this paper. 



[Table. 



