144 TRANSACTIONS LIVERPOOL BIOLOGICAL SOCIETY. 



because food is less abundant, or that small mussels form 

 a more nutritive diet than the other animals mentioned. 

 The latter conclusion appears reasonable, since the shells 

 of such small, rapidly growing mussels as were found in 

 the Barrow Channel plaice were, as a rule, exceedingly 

 thin. However this may be, there can be no doubt that 

 we have to deal, in the Bock Channel area, with small 

 plaice which are below the normal in condition. 



The graphs of the variation in value of the coefficient 

 k, which we may regard as a good index of the condition 

 of a plaice with regard to nutrition, appear to back up 

 this conclusion. All through the year the coefficient is 

 less, in the case of the Rock Channel plaice, than in 

 plaice either from Barrow Channel or from Beaumaris 

 and Red Wharf Bays; and in July the maximum is 

 attained in the two former areas, but it is much greater 

 in the northern than in the southern area. The conclusion 

 that the Rock Channel plaice are below the normal with 

 regard to condition appears to be so important that it is 

 desirable to examine critically the data on which it is 

 based. The values of the coefficient h represent variations 

 in the condition of the fish ; when the average weight 

 (the " condition ") of plaice of a certain length is 

 relatively high, h is also relatively high, and vice versa. 

 Each value of k in the table on page 179 is deduced from 

 weighings of a sample of fish varying from 40 to 150 in 

 number. Altogether about 1,100 plaice from Rock 

 Channel and about 740 from Barrow Channel were 

 weighed. When there are several determinations of k for 

 one month, the average is taken. The values of h found 

 in the table have been smoothed, and the graphs in 

 fig. 20 represent the monthly variation', of these 

 smoothed numbers. The arithmetic average of the value 

 of k, for Barrow Channel plaice, for the ten months, 



