PECQLIAKITIES OF PLAICE FROM DIFFERENT FISHING GROUNDS. 321 



of the Brown Eidges. If we take into consideration the small number 

 of specimens we see that there is a slight superiority over the latter. 

 The Plymouth specimens again, as far as we can judge from so small 

 a sample, appear to be a little shorter in the head than those of the 

 Brown llidges; in the males of these only the most frequent head- 

 length is 21, while in all the other cases the maximum is at 22. In 

 treating the samples in two sections only, southern and northern, we 

 see that the former are shorter in the head. When the numbers of the 

 two sexes are combined, the Norfolk coast sample appears to have the 

 longest head on account of the large number of females in this 

 sample. The greater length of head in the northern plaice is evident 

 when all the figures are combined into two columns. 



Caudal Peduncle. In this character a constant difference between 

 the sexes is not evident, but again a slight superiority in the northern 

 samples is indicated. 



Length of Caudal Fin. The caudal fin appears to be distinctly longer 

 in the sample from the Norfolk coast than in that from the Brown 

 llidges, the most frequent length being 19 per cent, in the former, 18 

 per cent, in the latter. The Plymouth specimens, however, have rather 

 longer tails, at least in the males, than those of the Brown Eidges, and 

 those of the north-east of the Dogger Bank rather shorter than those 

 of the Norfolk coast. I am inclined to think that a reduction 

 in the relative length of the caudal fin takes place as the limit of 

 increase in size is reached ; in other words, that the fin is shortest in 

 the oldest specimens, the caudal fin growing less than the body in adult 

 specimens, especially when the size reached is great. Thus two of the 

 three specimens of the Norfolk coast, in which the caudal fin is only 

 16 per cent, of the total length, are the two largest, 568 cm. and 

 63-0 cm. respectively. The Norfolk coast samples certainly include 

 more young specimens than any of the others, as well as absolutely the 

 smallest specimens examined, as is natural from the fact that the 

 district is nearest to the shore ; and in this sample the greater lengths 

 of caudal fin are most frequent. 



Number of Tubercles. This is a character which is not considered by 

 Duncker. Numerical characters are not usually subject to change with 

 growth in the individual, but this character may possibly change to 

 some extent. When one or more tubercles are so fiat as to be virtually 

 obsolete, I have counted only those which were distinct, while in other 

 cases some of the five usually present are represented by two or more 

 separate points. The flatness or prominence of the tubercles must be 

 considered, and it is not fully represented in the tables. 



In all cases the normal number 5 is most frequent. A reduction 

 occurs most commonly in the sample from the Norfolk coast ; it does 



