178 Dr. C. Liltken on the Vaag nicer and 



physiognomical differential characters, namely the more ele- 

 vated form of the body in T. arcticus, together with its shorter 

 and more suddenly contracted tail, in contradistinction to the 

 more elongated and more gradually narrowed tail in the fully 

 developed T. iris. Besides the northern seas, Trachypteri are 

 known from Chili and from the Indian Ocean ; but as to 

 their relations with the northern and Mediterranean species I 

 can say nothing positive ; it is probable, however, that they 

 are distinct from the latter, and that the Trachypteri in general 

 do not belong to the genera of deep-sea fishes the species of 

 which have, so to speak, a cosmopolitan distribution. 



As it has been attempted to distinguish two northern 

 species (T. arcticus and T. vogmarus) , it is not superfluous to 

 remark that the existing material certainly furnishes no sup- 

 port to any such separation, which must be absolutely rejected ; 

 and so far as this is founded upon the supposed observation 

 that certain Vaagma^rs are apparently askew or asymmetri- 

 cally formed, which has been stated in connexion with the 

 mode in which they have been seen to move through the 

 water, it must be remarked that I have found it impossible to 

 convince myself of the existence of this asymmetry in any of 

 the specimens investigated. So far as I can make out, it does 

 not exist at all, or, in any case, it is very inconsiderable. 



Of the other external characters of the northern Vaagmser 

 there were especially two which needed confirmation by the 

 comparison of a large series of specimens, namely : — 1, the 

 absence or the presence in the more or less adult Vaagmaer of 

 nuchal fins, or of the anterior part of the dorsal fin, always 

 apparently composed of five rays, of which part a rudiment is 

 certainly always present, but which has never been seen in 

 its full development in any northern Vaagmaer, as in general no 

 young stages of these corresponding to T. filicauda or T. 

 Spinolce are yet known ; and, 2, the absence or presence, as a 

 normal character, of the ventral fins 7 of which also we can in 

 general detect more or less distinct traces, but which have not 

 hitherto been found fully developed in any northern Vaagmaer. 



The answer to these questions is as follows : — In all the 

 twelve individuals from 0*935 to 2*200 metres in length, the 

 rays of the nuchal fin were broken off at the root, even 

 though the rest of the dorsal fin was in general perfectly well 

 preserved ; they were in part so concealed within the skin 

 that it was often difficult to count them ; and to all appear- 

 ance they had been lost very early, while the fish was still 

 quite young; they were, however, more distinct (8millim.) in 

 the thirteenth, still smaller specimen (0*830 metre long), the 

 youngest of the whole series. In this also distinct rudiments 



