BIHANG TILL K. SV. VET.-AKAD. HANDL. BAND 26. AFD. IV. N:0 8. 27 



cimen was caught in the river Karna and had perhaps there- 

 fore the genital organs more developed which may have in- 

 fluenced this measurement. The height of the caudal peduncle 

 in my speeimen is smaller than in Smitt's. 



The middle portion of the head (measured according to 

 Smitt's system 1. c.) is short, only 12 % of the total length. 

 The maxillary is in my speeimen smaller than in Smitt's and 

 measures only 29,4 % of the length of head. The interorbital 

 breadth is also smaller in my speeimen, namely 21,6 % of the 

 length of head. The horizontal diameter of the eye is about 

 13 % of the length of head, which is more than in Smitt's 

 speeimen. The length of the subopercle is, on the other hand, 

 a little larger, namely 31 % of the length of head. It can 

 be seen from this that there are some small differences with 

 regard to the relative measurements of these two specimens 

 although they are nearly of the same size. This can be ex- 

 plained as individnal variation or as sexual difFerence. If 

 the latter is the case, which however cannot with certainty 

 be decided on so little material, it looks as if the sexual 

 differences of the nelma and the belorybitsa should not be 

 parallel. If this is so it would help separate the two forms 

 from each other. As I have not had sufficient material I must 

 leave the question open as yet, but I am inclined to think 

 that the belorybitsa ought to be regarded as a, through iso- 

 lation, differentiated species or subspecies. Smitt draws the 

 attention to the similar condition with regard to Salmo flu- 

 viatilis and S. hucho. 



The belorybitsa only inhabits the northern part of the 

 Caspian Sea and ascends Volga and Ural river. In the Volga 

 system its spawning places are nowadays confined principally 

 to Karna with Ufa and other territories, according to Grimm. 

 Its food consists of small fishes as Ätherina, small herrings, 

 Gobiids etc, but also Pelecus. I opened the intestine and 

 stomach of many belorybitsas, but never found any parasites 

 in spite of the fish diet. 



Four species of herring may readily be distinguished in 

 the Caspian Sea. But of these only one is a true Clupea 

 s. str. namely: 



