which cause doubt apparently are encountered only on one host. Of the four 

 species of Dactylogyrus indicated for three fishes of two genera, two live 

 on fishes among whonn hybrids are known (D. vastator Nybelin, and D. 

 anchoratus Dujardin), 1--(D. robustus Malewitskaja) on two vicarious 

 (representative?, nobis) species, Leuciscus sp, and on Aspius aspius 



which hybridize with one of the preceding species. Finally the last 

 species--D. drjagini Bychowsky--is encountered on fishes of tv/o genera 

 close to each other among whom hybrids are still unknown but very pro- 

 bable. Two species encountered on four species of fishes of two genera 

 (D. linstowi Bychowsky and D. tuba Linstow) have fishes which hybridize 

 as hosts. 



D. minor Wagener and D. fraternus Wagener are encountered 

 on three species of fishes of three different genera and one of the hosts of 

 the first hybridizes with the two others, whereas the hosts of the second 

 all hybridize with each other. 



Most interesting are the last eight species of Dactylogyrus en- 

 countered on a large number of hosts relating to four or five genera, 

 specifically: D. nanus Dogiel and Bychowsky, D. similis Wagener, D. 

 sphyrna Linstow, D. cornu Linstow, D. crucifer Wagener, D. difformis 

 Wagener, D. fa 11 ax Wagener, and D. magnichamatus Achmerov. The 

 relations between the hosts of six species to each other and their ability to 

 hybridize and the character of the Dactylogyrus occurring on them is in- 

 dicated in figure 261. Hence, it is obvious that, with the exception of 

 D. nanus , the classification of all species strictly corresponds to the data 

 based on the presence of hybrids between the corresponding hosts. As 

 regards D. nanus, its finding on Leuciscus cephalus (L. ) will fit into the 

 scheme if it is discovered on Vimba vimba (L. ) or on Chondrostoma nasus 

 (L. ) or Alburnus alburnus (L. ), which seems very probable to us. From 

 the same scheme it is apparent that in all probability the same species 

 must be discovered on Alburnus alburnus (L. ) and Leuciscus leuciscus (L. ), 

 This is also substantiated by the fact that there are common species on 

 Leuciscus cephalus and AlburniE alburnus, for instance D. parvus Wagener. 



Dactylogyrus fallax Wagener is indicated erroneously in a 

 number of fishes in our work which was written during our student days 

 (Bychowsky, 1929). Actually, the hosts of D. fallax are related to the 

 genera of Abramis, Blicca, Rutilus, Leuciscus, and all form hybrids. 



D. magnichamatus Achmerov is encountered on six species: 

 Hypophthalmichthys molitrix (Val. ), Erythroculter erythropterus (Bas. ) 

 Er. mongolicus (Bas. ), Culter alburnus Bas. , Hemiculter leucisculus 

 (Bas. ), and Megalobrama terminalis (Rich. ). At first, one specimen of 

 this species was discovered on the first species of host, and described from 

 it by A. H. Achmerov in 1952. Subsequently it was discovered by A. V. 

 Gussew on all the rest of the hosts, but he never once found it on 



268 



