that the mysterious form of A. baikalense is the same species as T. borealis 

 Olsson. As regards the "suckers" on the disc of Ancyrocotyle it is true that 

 during careless examination of individual specimens one can notice on the 

 separate lobe --shaped outgrowths of the disc certain evaginations which 

 resemble suckers but which actually have nothing to do with them, in 

 connection with which the drawings and the description of Vlassenko are 

 the result of a certain imagination because of an insufficient familiarity 

 with the group. Unfortunately our data were not published, -^ which led to 



1 



The only reference to them is in the work of V. B. Dubinin (1936) 

 where the author states that the genus Dactylodiscus is made synonymous 

 with Tetraonchus and the species D. borealis Olsson is transferred into 

 the latter. 



a certain regrettable error in the resume' of Sproston. 



Finally, in 1948 Bauer published a special article in which on 

 the basis of his, and especially our data, he indicates that Ancyrocotyle 

 baikalense is equivalent to Tetraonchus borealis. One must note, however, 

 that in this work he commits a number of errors based on a insufficient 

 knowledge of the corresponding literature. 



Thus, the question about the "genera" of Dactylodiscus and 

 Aviella at the present time can be considered completely solved. One 

 must also note that very recently a number of species of Tetraonchus 

 from different Salmonidae and Thynaallidae were described (Price, 1937; 

 Bauer, 1948b; and others). However, because of considerable individual 

 variability of the representatives of the present genus it seems probable 

 to us that many of these species have no right to existence and possibly 

 there is only one species, T. monenteron, which has different forms on 

 different hosts. However, this supposition demands substantiation by 

 statistical methods or even by experimental means. 



2. Family Amphibdellatidae (Carus, 1885) 

 Bychowsky emend. 



(Figs. 284, 285) 



Amphibdellidae Carus, 1885; Gyrodactylidae Cobbold, 1877, 

 part. ; Dactylogyridae, Bychowsky, 1933, part. ; Tetraonchinae Monticelli, 

 1903, part . 



Tetraonchidae, having small sizes in the adult state. Attaching 

 apparatus consists of a chitinous armature with 16 edge hooks, 2 pairs of 



467 



