'6'12 PECULIARITIES OF PLAICE FROM DIFFERENT FISHING GROUNDS. 



not occur in the specimens from the Brown Eidges, but is more common 

 in the Plymouth specimens than in those from north-east of the Dogger 

 Bank. 



The description " flat," however, in reference to the tubercles, occurs 

 frequently among the notes of examination of the specimens from 

 beyond the Dogger Bank, and least frequently in connection with the 

 Brown Eidges specimens. The reduction of the tubercles, which makes 

 some of them virtually obsolete and the rest less prominent, was 

 particularly noticed in the largest females from the Norfolk coast, 

 especially in a sample sent me in November, and caught fourteen miles 

 off Cromer. In many of these I thought the condition suggested that 

 the tubercles had actually been subject to mechanical friction. In the 

 same specimens the edges of the marginal fins were thickened 

 and contracted, evidently in consequence of frequent abrasion and 

 healing. We know that the ground off the Norfolk coast is very rough 

 and stony, and that the plaice is in the habit of burying itself in the 

 ground it lives on. The fish also must doubtless push its head under 

 stones and into the ground to obtain its prey ; so that I think it very 

 probable that the tubercles, as well as the edges of the fins, are worn 

 away in the plaice of this district. The ground on the Brown Eidges, 

 on the other hand, is composed of exceedingly fine smooth sand ; that 

 beyond the Dogger Bank is rather smooth ; and on the Plymouth 

 grounds both rough and smooth occur. 



Gill-rakers. In all cases the most frequent number of the anterior 

 processes on the first branchial arch is 10, and there is not much 

 difference in this character between the sexes or the samples from 

 different localities. But there is seen in the females of the Norfolk 

 coast a slight indication of an increase in the number; the numbers 

 above 10 occur more frequently in proportion. Considering the large 

 number of female specimens from the locality which were examined 

 (91), this result is, I think, significant, and it is confirmed by a similar 

 indication in the females of the most northern locality. We may infer 

 that the number of gill-rakers increases as we proceed towards the 

 north. 



Fin-rays. The variation in the number of fin-rays is considerable, 

 and the frequencies of the different variations are not very symmet- 

 rically distributed. The largest sample is that of the females of the 

 Norfolk coast, and here the most frequent number in the dorsal fin 

 is 72 ; but the middle frequency, which is almost as great, is 73. The 

 most frequent number in the males is 74; but, nevertheless, it will 

 be seen that on the whole the number of fin-rays is greater in the 

 females than in the males in all the samples; that is to say, in tlie 

 former the higher numbers occur more frequently, and the lower 



