324 PEUULIAKITIES OF PLAICE fllOM DIFFERENT FISHING GliOUNDS. 



study the developmeut of the spiuulatiou on the scales. In a specimen 

 207 cm. long, and another of 238 cm., there was no trace of spines on 

 the scales of the fin-rays, while in another 25"8 cm. long they were just 

 developing. In most cases there are not more than two spines on each 

 scale, and on many scales only one spine. The spine commences as a 

 deposit of calcareous matter in the shape of a short cone, and is formed 

 not as an outgrowth from the scale, but as a separate deposit, of which 

 the base afterwards becomes united to the scale. The position and 

 shape of the growing spine are shown in Fig. 1. 



In the table of the frequencies of the degrees of spinulation I have 

 omitted those specimens from the males of Norfolk coast and the Brown 

 liidges which were below 26 cm. in length. In the former case there 

 were eight of these, leaving 41 to be considered; in the latter there were 

 only two omitted, leaving 50. It will be seen that in both cases the second 

 degree of spinulation is the most frequent, but it is equally evident 



Fig. 1. 



Scale of dorsal fin-ray of a plaice from the Norfolk coast, 25 "8 cm. long, magnified. 

 S the incipient spine at the outer edge of the scale. 



that the higher degrees are somewhat more frequent in the specimens 

 from the Norfolk coast. Now among the latter the smaller specimens 

 must be younger and more immature than those of the same size from 

 the Brown liidges, and therefore the lower degrees of spinulation ought 

 to be more frequent in the specimens from the Norfolk coast, if we 

 consider only those which do not exceed the maximum length of those 

 from the Brown liidges. One specimen, however, of the three from the 

 Norfolk coast which had no spinulation was actually mature — it was 

 36"5 cm. long ; the other two were apparently immature, and were 

 smaller. This shows that the development of spinulation does not 

 always correspond exactly to the attainment of maturity, although it 

 does so usually. In the Norfolk coast sample there are 12 specimens 

 exceeding in size the largest of the Brown liidges plaice ; the largest 

 of these 12 is 48'9 cm. long, the next largest is 43*2 cm. Putting aside 

 the largest, we cannot consider the other 11 to be older than any of the 



