L 



TRANSACTIONS OF SECTION D. 903 



of the U.S. Commission of Fish and Fisheries. The remainder, 1,529 in all, 

 have heen taken at various points round the British Isles — 400 in the North Sea 

 (off Lowestoft and Bamsgate), 300 near Plymouth, 74 off the Scilly Isles, 100 near 

 Brest, and 655 off the S.W. coast of Ireland (Kinsale and co. Kerry). The 

 Irish fish are further divisible into 310 autumn fish and 345 spring fish. 



The chief characters chosen for examination were : — 



A. — The number of black transverse bars or stripes on one side (the left) of 

 the fish. 



B. — The number of transverse bars on one side (the left) which cross or meet 

 the lateral line. 



C.— The presence or absence of round black spots ('intermediate spots') 

 between the bars of series A. The variation of this character is tabulated under 

 two heads : — (1) The number of fish per centum which possess one or more of 

 these intermediate spots, and (2) the total number of such spots per hundred fish 

 (the left side only of each fish being considered). 



D. — The number of rays in the first dorsal fin. 



E. — The number of rays in the second dorsal fin, including any incipient fin- 

 lets which are still partially connected with the fin by a low web or ridge, or 

 which are merely closely approximated to the fin and erectile with it. 



F. — The number of dorsal finlets, including all incipient finlets described 

 under E. 



The accompanying table shows the results of this examination. The mean 

 values of each character for the total number of fish from each locality are 

 expressed in terms of the general mean, as + or — deviations from the value of 

 that mean. The general mean value of each character is the arithmetic mean of 

 all the observed values of that character, the American data alone excepted. The 

 American mean values for several of the characters, especially A, B, C, and F, 

 differ to such an extent from the British means, that there can be no further doubt 

 as to the existence of racial peculiarities which distinguish American from British 

 specimens of the mackerel. As compared with the British mackerel, the American 

 fish possesses the following racial characteristics — (1) A higher number of trans- 

 verse bars, (2) much greater spottiness, (3) a smaller number of fin-rays in the 

 second dorsal fin, and (4) a greater number of dorsal finlets. These characteristics, 

 it must be borne in mind, are average distinctions, and do not suffice to dis- 

 tinguish every individual. But, I may add, they are so marked in the present 

 case, that on examining a sample of a dozen fish at Toronto during the last 

 meeting of this Association, I became there and then convinced of the existence 

 of racial peculiarities in this species. 



With regard to the British fish, the range of variation is very limited, espe- 

 cially in the case of the second dorsal fin, the greatest deviation from the general 

 mean value of which does not amount to ^ of a fin-ray in any sample of lOQ 

 fish. The total number of fish from the various localities is seen to be insufficient 

 in this case to afford a basis for the establishment of racial differences. In the 

 case of the first dorsal fin the variation is greater, but here the difficulty of 

 accurately determining in all instances the exact number of fin-rays present 

 ;(owing to the extreme minuteness of the posterior rays) has also provided an 

 obstacle to very definite results. Nevertheless the characters A, B, C, and F, the 

 variation of which has been seen to be so marked in the American fish, also pro- 

 vide sufficient data for separating the British fish into at least two groups of 

 different racial tendency. These groups are — (1) fish from the North Sea and 

 ■English Channel, and (2) Irish fish, both autmnn and spring forms. The table 

 shows that fish from the North Sea and Plymouth agree in the following points— 

 (1) the mean number of transverse bars A and B is below the general average, 

 'and (2) the mean number of spotty fish and of intermediate spots is above the 

 general average. Moreover, the mean number of dorsal finlets was below the 

 average in the case of 300 fish from Lowestoft and 300 from Plymouth, although 

 remarkably above the average in the case of 100 fish from Ramsgate. 



On the other hand, the autumn and spring forme of Irish fish agree in the 



