6 E. LÖNNBERG, THE ICHTHYOLOGY OF THE CASPIAN SEA. 



the second dorsal fin is considerably smaller in the Caspiau 

 than the corresponding measurements in the common and in 

 the Volga-pikeperch. 



The base of the anal fin is enlarged vvith age in the 

 common pikeperch and seems to exceed that of the other 

 forms of corresponding size. 



The pectoral fins are comparatively longer in the young 

 specimens and in the males, but are diminished with age. 

 Considering that the specimen of Stizostedium marinum, mea- 

 sured above, although a female, has larger pectoral fins than 

 a male St. lucioperca of nearly the same size, it seems, as if 

 the reduction of the pectorals should not be quite as strong 

 in the former. In this respect St. volgensc has conspicnously 

 retained juvenile characters. The same relation ship prevails 

 with regard to the ventral fins with the difierence however 

 that the juvenile characters in St. rolgense are still more 

 pronounced here, but a little less in St. marinum. 



The comparison of the horizontal diameter of the eye 

 with the length of the head shows that the eyes are com- 

 paratively smaller in older and larger specimens of St. lucio- 

 perca. St. volgense has retained the juvenile character of large 

 eyes, but in St. marinum the development has gone in quite 

 an opposite direction. 



Other differences that can be seen from the above table 

 are as foUows. St. caspium has the distance between the 

 snout and the dorsal fin and between the snout and the 

 ventral fins larger than in the other forms, which are rather 

 similar to each other in this respect. But on the other hand 

 St. volgense and caspium agree in having the relation between 

 the least depth of the body and the total length greater than 

 the same in the common pikeperch. This is a masculine 

 character as can also be seen on the table över the measure- 

 ments of St. volgense. 



From these relative measurements it can be seen that 

 the -development of these three forms of pikeperch has gone 

 in different directions.^ St. volgense is apparently a weaker 

 form which has retained juvenile and masculine characters in 



' Mr. G. A. BouLEXGER has drawu the attention to the affinity between 

 the Caspian pikeperch and the North American St. canadense (.conf. Proc. 

 Zool. Soc. 1892 Part. III p. 411—413) and I take the pleasure of referring 

 to this account. 



