252 MR. R. COLLETT ON BAL^NOPTERA BOUEALIS. [Feb. 2, 



VI. Flippers and other External Characters. 



The Flippers are relatively shorter than in any of the other species, 

 somewhat slender and pointed. Their length, measured from the 

 axilla, is about one eleventh of the total length, occasionally a little over 

 and sometimes under this measurement. In form they do not differ 

 materially from those of the other species. A little beyond the 

 middle they present on the ulnar side a slight extension, an indication 

 of the commencement of the manus. At this point the flippers have 

 their greatest breadth, which is, compared to their length (reckoned 

 to the axilla), as 1 to 3-5 or 3-6 (or to caj)ut humeri as 1 to A-7)- 

 Thus in its small flippers B. borealis differs essentially from B. sib- 

 baldi, which it otherwise resembles in so many points, and approaches 

 nearer to B. mvsculus. Their colour, as previously mentioned, is 

 essentially the same on the outer and inner sides, and in this respect 

 they differ from all the other species, in which the inner side is more 

 or less white. 



The Dorsal Fin is situated far forward and is high. The front 

 margin is convex, with a slightly curved apex ; its hinder margin 

 is deeply concave. In form and position it is quite unlike that of 

 B. sihbaldi and B. musculus, and is most like that of B. rostrata, 

 but it lies further forward than in any of them. Tlie following 

 are the proportions between the total length of the body and the 

 distance from the end of the snout to the beginning of the dorsal fin 

 ia five of the specimens examined by me : — 



No. 1.. As 1 to 0-65. 

 No. 3. . As 1 to 0()8. 

 No. 4. . As 1 to 0-6.T. 

 No. 6 . As 1 to 0-G5. 

 No. G.. As 1 to (i-Gl. 



The dorsal fin is thus constantly placed anterior to the com- 

 mencement of the last third of the body, whilst that of -B. rostrata 

 (according to Sars) is placed at the beginning of this tbird ; it is 

 even furtlier back in B. musculus, and furthest back in B. sibbaldi. 



Its height and size is on the whole considerable, especially in 

 comparison with the length of the flippers. The height is in fact 

 more than Ij times the greatest breadth of the fli{)pers, and is to 

 their length as 1 to barely 2|. The dorsal fin is possibly higher in 

 the male than in the female, although the difference cannot be 

 great. 



The length of the anterior margin is about the same as that of 

 the base. 



The Flukes, in a couple of specimens examined by me, were, com- 

 pared to the total length of the body, as 1 to 4"2. 



Thus they were relatively somewhat smaller than in B. rostrata 

 (3"4), b>it larger than in B. musculus (4'1-5'1). 



Their colour is, as in B. sibbaldi, about the same on the upper 

 and lower sides. 



The Anus is situated directly under the apex and posterior margin 



