188G.] MR. R. COLLETT ON BAL^NOPTERA BOREALIS. 249 



the narrowest point (just where the flukes commence) was in the 

 largest specimen 390 mm., or about 15 inches. 



V. Colour. 



The colour of the back is bluish black or occasionally some- 

 what brown, much resembling the colour in B. sibbnldi, although 

 the blue colour as a rule is less pronounced than in that species. 

 The colour after death is darker than in the living animal. On the 

 side of the body the colour becomes somewhat lighter ; the belly is 

 dark steel-grey with a white area running along the centre ; the 

 white colour begins at the symphysis of the lower jaw, and termi- 

 nates at the genitalia, but occasionally it is interrupted or imper- 

 ceptible on the middle portion of (he belly. 



Considerable variations occur in the breadth, size, and form of this 

 white part of the belly. The throat is always white, occasionally 

 throughout its entire breadth,, sometimes only for a couple of feet. 

 On the breast the white becomes narrower, and in many indi- 

 viduals is completely cut off by the bluish-grey colour of the sides, 

 but it then reappears on the belly, and continues in a somewhat 

 irregular width to the genitalia. Behind the vent the whole under- 

 side of the tail is hght bluish grey, about the same as the back. 



The white colour is not always symmetrical, but is occasionally 

 broader on one side of the middle line than on the other; also the 

 extent of it on the belly may be rather irregular. On the throat 

 similarly the white colour is sometimes broader on one side than on 

 the other. 



The white patch on the belly was never absent in any of the 

 specimens examined ; and this observation is confirmed by all the 

 managers of the whaling companies, who state that it is always to 

 be found, though it is sometimes only slightly developed. 



The white colour, especially on the throat, is pure and sharply 

 defined. On the belly and in front of the genitalia there are, on 

 the contrary, a large number of very fine bluish-grey lines, which 

 are quite short and run parallel to each other ; tliese lines, which 

 can only be distinguished when you are near to the animal, some- 

 times, when they are very numerous and closely set, detract from the 

 whiteness of these portions. 



The flippers are coloured on the outer side like the back ; on the 

 inner side they are a trifle hghter, especially along the lower edge : a 

 few indi\idua'ls (such as No. 2 of the specimens examined) have large 

 whitish spots on the inner side ; these are never, however, absolutely 

 white. The flukes of the tail are also bluish grey underneath ; the 

 dorsal fin is exactly the colour of the back. 



Distributed over the dark parts of all the specimens examined , 

 were a greater or less number of whitish oblong spots of peculiar i 

 form and colour, their length being about 100 mm., and breadth 

 about 30 (Plate XXVI. fig. 2). Their outer edges are not always 

 sharply defined ; their colour is in general whitish grey, occasionally 

 almost white, and more rarely dark grey. Along the centre of the 

 Proc. Zool. Soc— 188C, No. XVII. 17 



