It is necessary to say a few words about the synoymy of the 

 genus Tetraonchus. Omitting the fact that until recently this genus was 

 confused with the genus Ancyrocephalus, now including representatives 

 of the second in the first and now, conversely; one should not be sur- 

 prised that until the present time the question about the independent 

 existence of the "genera" Dactylodiscus Olsson, 1893 and Aviella Sproston, 

 1946 {=Ancyrocotyle Vlassenko, 1928) is still being discussed. Even in 

 the beginning of the 20th century Monticelli in two of his works (Monticelli, 

 1903, 1905) indicates that the genus Dactylodiscus is synonymous to 

 Tetraonchus; however, at the same time the author considered both 

 Ancyrocephalus and Amphibdella as synonymous to the last genus, this 

 did not sound convincing although it corresponded to the truth as will be 

 shown later. 



In 1937 in the re'sume'of Price the genus Dactylodiscus is left 

 as a genus inquirendum with the indication that Johnston and Tiegs (Johnston 

 and Tiegs, 1922) ascribed it as a subgenus to Ancyrocephalus without 

 sufficient basis. In her re'sume' Sproston leaves Dactylodiscus without 

 special examination indicating the opinions of the above-mentioned authors. 

 Finally in 1952 in one of the works of Brinkmann (Brinkmann, 1952a) the 

 author indicates that Nybelin found JD. borealis Olsson (only species of the 

 "genus") in Norway. One must point out that in 1928 Vlassenko described 

 a new species and genus Ancyrocotyle baicalense (sic) which sharply differs 

 from all the known forms of Monogenoidea by the presence of a primitive 

 internal organization and a complex attaching disc with 6 suckers and 4 

 middle hooks. On the basis of the description of Vlassenko, Sproston 

 separated the present form into a special family Aviellidae ^ in her re'sume"^ 



1 



Sproston replaced the name of the genus given by Vlassenko which was 

 a homonym of Ancyrocotyle Parona and Monticelli (sic), 1903 by Aviella 

 Sproston. 



establishing at the same time a special superfamily Avielloidea linking the 

 last with Polystomoidea and Diclidophoroidea. 



In 1934 we received from V. B. Dubinin material on Mono- 

 genoidea from Thymallus thymallus (L. ) (typical host of Dactylodiscus 

 borealis) from the river Pinega in the region of Archangel. During the 

 study we succeeded in establishing that on it are representatives of the 

 species described by Olsson and, at the same time, that this species is a 

 typical representative of the genus Tetraonchus ,!. e. , the genus p. 390 



Dactylodiscus has no right to existence and is synonymous to the first. 

 Further, in 1936, having become interested in the "genus" Ancyrocotyl e we 

 collected material of this genus from the same host and from the same 

 region from which the collections of Vlassenko were made and we explained 



466 



