372 Part III. — Twentieth Annual Report 



size of 78-6 mm., or 3^ inches. On 27th November 1900, 125 ranged 

 from 68 to 108 mm., and had an average length of about 81 mm., or 3/^ 

 inches. On 30th December, sixty-two, ranging from 67 to 98 mm., had 

 a mean lengtli of 84*8 mm., or 3| inches. 



THE LONG ROUGH DAB {Drepano2Jselia platessoides, Fabr.). 



Collections of this species were obtained by the fine-meshed net from 

 deep water off the Shetlands, from the Moray Firth, the Firths of 

 Clyde and Forth, and from deep water oflf the coast of Aberdeen. 



1. Off the Shetlands. 



The hauls in the deep water in the northern part of the North Sea 

 were made in August, September, and October 1900, and in May and 

 December 1901. 



In two hauls on 31st August and 4th September, in 62 and 65 

 fathoms, about 65 miles S.E. by E. from Sumburgh Head, 3202 

 long rough dabs were caught and measured. The sex of those obtained 

 in the first haul was not determined, but in the second haul the sexes 

 were distingviished and their measurements separately recorded. 



In each case two groups were very clearly represented, the first 

 being distinctly marked off from the second by a considerable interval. 

 In the haul of 31st August there were 20 specimens belonging to the 

 first series, measuring from 28 to 57 millimetres; with a range of 

 29 mm., and an average size of 48'3 mm., or Ig inches. In the haul 

 on 4th September 244 fishes of this series were obtained, ranging in 

 length from 31 to 63 mm., and with an avex-age size almost precisely 

 the same — viz., 48 "4 mm. These fishes were the brood of the year, 

 probably about six months old, and their small size after a summer's 

 growth attests the slow development of this species. Moreover, an 

 examination of the grouping in which they are arranged in 

 2 -millimetre groups, or of a curve constructed on that grouping, shows 

 that the smallest individuals are not adequately represented (consider- 

 able numbers having no doubt escaped through the meshes of the net), 

 and that the average size is more probably under 46 mm. 



The second series or gi'oup was also very well differentiated in each 

 haul, separated from the younger group by a blank interval of 25 mm. 

 and 14 mm. respectively, but overlapping slightly the next older group. 

 In the collection of 31st August the series (sexes mixed) commences 

 at 82 mm. and extends to about 122 mm. The average size of the 551 

 fishes composing the group was found to be 103*2 mm., or 4-^ inches, 

 the range being 40 mm. between the smallest and the largest. In the 

 second haul the sexes in this and the following series were distinguished. 

 Of the 1334 fishes forming the group, 782 were males and 552 

 were females. The males ranged in length from 77 mm., or very 

 slightly over three inches, to 119 mm., or 4r| inches, the diflfei-ence 

 between the largest and smallest being 42 mm., or If inches. The 

 average size was 102 mm., or 4 inches. The females measured from 

 82 mm., or about 3^ inches, to 128 mm., or slightly over five inches, 

 the difference in size between the lai-gest and smallest being 46 mm., or 

 lif inches. The average size was 105-8 mm., or slightly over 4g 

 inches. The females were thus somewhat larger than the males ; 

 they grow faster, as I have already explained. If the measurements of 

 the males and females are combined the termination of the mixed 

 group is found to be precisely as in the haul four days earlier — viz., 



