82(3 PECULIARITIES OF PLAICE FPvOM DIFFERENT FISHIISG GROUNDS. 



distinct diflerences in structural characters between the samples, 

 especially between those of the Norfolk coast and the Brown Kidges, 

 which would almost certainly be confirmed by examination of a larger 

 number of specimens. 



Omitting the tubercles and the length of the caudal peduncle, in 

 which the indications are not very distinct, I find distinct differences 

 in the following characters : Height of body, length of head, length of 

 caudal fin, spinulation of scales, number of gill-rakers, number of fin- 

 rays. The length of the caudal fin decreases apparently with age, and 

 it is not very evident that it is a permanent characteristic of the 

 different local forms. We have then left three characters of proportion 

 and two of number. The first three characters all vary with age, the 

 latter two do not change in the individual. 



The change in the height of the body with age does not appear to be 

 very constant or important in my samples ; the height is distinctly 

 greater in the northern samples than in the southern. The difference 

 between the sexes is slight. 



The length of head is a marked sexual character, being greater in the 

 females ; it decreases as age advances, but within the limits of size 

 of my specimens the decrease is not obvious in the females, and not 

 very important in the males. The length of head is a little greater 

 in the northern samples. 



The spinulation of the scales is a character, with few exceptions, 

 confined to mature males, and forms the most conspicuous local 

 peculiarity. There is no important difference in this character between 

 the plaice of Tlymouth and those of the Brown Eidges; but on the 

 Norfolk coast, and still more beyond the Dogger Bank, it is much more 

 developed than on the Brown Ridges. 



The number of fin-rays is slightly greater in the females, and is 

 somewhat less in the northern samples than in the southern. 



The gill-rakers, on the contrary, are slightly increased in the northern 

 samples as compared with the southern. 



II. Comparison of the Local Forms Examined with those 



OF other li eg ions. 



Duncker examined 35 males and 45 females caught in the neigh- 

 bourhood of Heligoland. The males were from 13-4 cm. to 289 cm. 

 in length, the females from 19-3 cm. to 32-6 cm. Now I have shown 

 in a previous paper that no plaice from this district were mature below 

 11 in., or very nearly 28 cm., in two samples which I examined, con- 

 taining together 307 specimens. It is not surprising, therefore, that 

 in Duncker's specimens the degree of spinulation was much lower than 



