the present time, that is they are monotypical (Table 8). There is no 

 doubt that these genera cannot have special significance in the discussion 

 about the normality (for other possible meanings of this word, see above, nobis) of occurrence 

 of the Monogenoidea on the families of their hosts because in a number of 

 cases we deal only with single findings. However, even among this group 

 there are genera which are often found and w^hich strictly occur only on 

 fishes of one family, and this, either on one species, as for instance 

 Liinguadactyla , Paradiclybothrium, or even on several--Bychowskyella, 

 Protancyrocephalus and others. More interesting are the following 28 

 genera which contain several species and each parasitize one family of 

 fishes (Table 9) and in such a fashion demonstrate more convincingly that 

 here occur normal connections between the genus of the parasite and the 

 family of the host. For 23 genera of monogenetic trematodes it is in- 

 dicated that they occur on two families of fishes (Table 10). During the 

 examination of this group of genera we see that part of them parasitize 

 close, more or less related families of fishes, and part on those which 

 have absolutely no phylogenetic connection between them whatsoever. One 

 must note that the related families of fishes on which certain genera of p. 252 



Monogenoidea are parasitic are in different degrees of consanguinity with 

 each other. Thus some, as for instance Siluridae and Bagridae, Cyprinidae 

 and Cobitidae, Acipenseridae and Polyodontidae, Carcharhinidae and 

 S yliorhinidae etc. are very close to each other, whereas other families, 

 even though they are related, are distantly so. For instance Trigonidae 

 and Myliobatidae or Squalidae and Carcharhinidae and others can be placed 

 in the latter group. Finally the hosts of Gastrocotyle and Plectanocotyle 

 are in more distant consanguinous relations. For the hosts of Gastrocotyle, 

 Carangidae and Scombridae, the consanguinous relations are not even 

 recognized by everybody; however, as we have already indicated Gregory p. 253 

 (Gregory, 1951) is undoubtedly right when he unites Carangidae, Scombridae 

 and certain other families w^ithin the group Scombroidei; the data on 

 parasitism fully agree with his co^^clusions as will be seen later. 



The representatives of distant families of Perciformes are also hosts for 

 Plectanocotyle, One must say that if one species (P^ gurnardi Ben, and Hesse) is often 

 encountered on different Trigla then the second (P^ elleptica Dies. ) was encountered 

 only by Dlesing (Dieslng, 1850) and actually it should be considered as practically 

 undescribed and possibly not even belonging to the given genus. 



Special interest is occasioned by the examination of those genera of Mono- 

 genoidea as hosts of which were Indicated two families of fishes not connected to each 

 other by consanguinous relations. Let us examine these genera. Anchylodiscus is en- 

 countered in Australia and only one species- -A. gadopsis Hughes- -is indicated for 

 Gadopsis species. 1 We have no basis whatsoever to doubt the determination of the host; 

 however, it is not clear whether A^ gadopsis is a representative of the genus 



285 



