576 LÖNNBERG, OBSERVATIONS ON CERTAIN PLAT-FISHES. 



also. The second ray is also repeatedly bifidate but not so 

 deeply so and therefore does not get so broad. The next four 

 rays are twice bifid, but less deeply so still. The seventh and 

 those following are only bifid at the tip. The first rays project 

 with their branched ends beyond the web, of the fin, as in the 

 brill. Thus the fin-membrane only extends along the proximal 

 half of the anterior margin of the first ray and along the prox- 

 imal third of that of the second ray etc. Thus the first branched 

 rays of the dorsal are rather loosely connected together and 

 very movable, and form a kind of tentacular organ. 



We have thus an almost complete and very interesting 

 series, showing the development from the simple dorsal rays of 

 the turbot to the very complicated ones of the brill. In size as 

 well this series of the five hybrids shows an increase and deve- 

 lopment. The three first specimens (N:s 1, 2, 3) have the size 

 of the first dorsal ray varying from 3,3 — 3,5 % of the total 

 length of the body, in N:o 4 it is 4,3 Yo and in N:o 5 5,3 %. 



The average length of the first ray of the dorsal seems to 

 vary in the turbot from 3,1 to 3,2 % of the total length, and in 

 the brill from 5,5 to 5,8 %. The measurements taken from the 

 five hybrid specimens therefore give an intermediate and pro- 

 gressive series for the size also, of the first dorsal ray. 



The curve of the lateral line, on the contrary, in these 

 five hybrids does not show any progressive series. "The height 

 of the abdominal curve of the lateral line, above the line from 

 the beginning of the lateral line behind the temporal region to 

 the beginning of the straight part", is 



in N:o 1 38 »/» of this line 



» » 2 27 ?^ » -> » 



» » 3 AÜ % -» » » 



» »4 M) % y> » » 



» » 5 38.^ » » ». 



Thus N:o 2, which is one of turbotlike forms, has the raost 

 brill-like lateral line. N:o 3 is a turbot-like hybrid and that it 



