Eleven genera-- Cathariotrem.a , Pricea , Gotocotyle, Hexostoma , 

 Heterocotyle, Lamellodiscus, Megalocotyle , Qctostoma , Tetraonchus, 

 Tetrancistrum, and Tristoma--are discovered on three families of fishes of 

 one order. Practically all these genera parasitize more or less related 

 families of fishes, for instance, Tristoma , Gotocotyle and Pricea parasitize 

 the Scombroidei (according to Gregory); whereas Octostoma basically 

 parasitizes the same hosts (it is also indicated for Sciaenidae). Only three 

 genera--Cathariotrema, Hexostoma, and Tetraonchus --warrant special 

 remarks. The first of them- -monotypical--is encountered on three families 

 of sharks which are very close to each other (see page 230). The second is 

 interesting in the fact that one of the eight of its species (H. grossum ) p. 268 



parasitizes representatives of two families of hosts --Carangidae and 

 Thunnidae underlying by this very fact their consanguinous ties and, what 

 is most important for us, substantiating once more the proximity of 

 Carangidae to the rest of the Scombroidei as is accepted by Gregory. 

 Finally, we have already written about the genus Tetraonchus (page 256 ), 

 and its occurrence is an excellent illustration which substantiates the point 

 of view of L. C. Berg concerning the relations of Salmonidae, Thymallidae 

 and Esocidae. 



Finally, 16 genera- -Gastrocotyle, Echinopelma, Hexabothrium , 

 Plectanocotyle, D iclybothrium, Lithidocotyle, Monocotyle , Gyrodactyloides , 

 Squamodiscus, Octomacrum, Pseudohaliotrema, Ancylodiscoides, Diplozoon, 

 Discocotyle, Microbothrium and Thaumatocotyle--are encountered on two 

 families of fishes of one order. The hosts of these genera are generally 

 sufficiently related with the exception of the hosts of Plectanocotyle -- 

 Serranidae and Triglldae. As a matter of fact, however, this is the only 

 case of the simultaneous occurrence of the representatives of one genus of 

 monogenetic trematodes on these two families of fishes. 

 Species of the genus Choricotyle were also found on them, whereas the 

 representatives of the genus Trochopus are also encountered on the families 

 close to Serranidae --Scorpenidae and Triglidae. Apparently there must be 

 closer genetic links between Triglidae than is usually believed. As a matter 

 of fact, the presence of these links is clearly apparent in the phylogenetic 

 scheme of Gregory to which we have often referred. 



Summing up the totals of the examination of Table 15 (the 

 occurrence on one family of fishes) does not demand special commentary. 

 We see that a vast majority of genera of monogenetic trematodes is either 

 encountered on one family of fishes (100 genera) or on a group of families 

 related to one or even two and more orders but which are related to each 

 other (40 genera). The degree of consanguinity of the families of hosts is 

 very different, as is understandable, but at any rate it shows the phylo- 

 genetic proximity of these families or even the orders in which these 

 families belong. Only eight genera of Monogenoidea are found in unrelated 

 groups of fishes (which is the most interesting for our analysis). The 

 discussion about their occurrence; which was cited above shows that among 



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