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



latter. The prseorbital leiigth is in both increasing witli age, 

 .hut the pöstorbital decreasiiig. With regard to the latter 

 dimension the såpa ^ represents a stage more advanced in the 

 direction of developmeiit of these forms, than the hallcnts 

 does. The height of the body is comparatively larger in the 

 såpa which in this respect more resembles the bream. The 

 såpa has also a broader caudal peduncle. The distance be- 

 tween the snout and the dorsal whieh increases with age 

 and between the snout and the anal fin is also larger in the 

 såpa which accordingly in this respect, too, stånds nearer to 

 the bream-type. The same can be said about the percentage 

 expressing the relation of the preeabdominal length. The re- 

 lative length of the pectoral lins decreases with age in both 

 forms, but this measurement is larger in the sa/)a which in 

 this is intermediate between the hallerus and the bream. The 

 shortness of the base of the dorsal fin is one of the charac- 

 teristics through which sa23a and hallerus distinguish them- 

 selves from the bream-type. This is, however, not so pro- 

 nounced in the former. The length of the base of the anal 

 fin is comparatively the same in both forms. The charac- 

 teristics which separate these two forms from the bream-type 

 are the following: the small head, the slender form of the 

 body, the short distance between the snout and the vertical 

 fins, the short preeabdominal length, the small dorsal and 

 pectoral but large anal fins. From the comparison above it 

 becomes evident that Ahramis såpa only possesses the first of 

 these characteristics in a higher degree than, and the last in 

 ' the same degree as Ahramis hallerus, but in all others it is 

 less specialised than the latter. 



The individuals from which the above measurements have 

 been taken were collected in the Volga delta. 



Pelecus cultratus Lin. 



I collected specimens of this stränge looking fish the 

 s^tschechon» in the Volga delta in the spring (end of April 

 and May) when it ascended with other fishes. The largest 

 specimen I saw measured 42 cm. 



* For shortness sake såpa is here used for Ahramis såpa Pallas which 

 in Rnssian is called sbeloglaska», but it is Ahramis hallerus which is called 

 in Russian »sopa» or »såpa». Pallas has thns made a mistake and mixed up 

 the Russian names. 



