(Cypriniformes--2 species, Perciformes--! sp. ). Enough has been said 

 above about relations of Dionchus (see page 256 ). We see similar relations 

 ?.mong Heterobothrium (en TetrodontiforTnes--! species, and on Pleuronecti- 

 formes--l species), but it is possible that this genus was created artifically 

 and then the occurrence of the possible two genera really has a "normal" 

 character. 



The two genera Diclidophora and Metahalictrema were dis- 

 covered on two families of two orders of fishes. For the first of these 

 genera the occurrence en closely related orders of hosts is characteristic 

 (see page 225 ), and on one, in the vast majority of the species (Gadiformes-- 

 10 species of Diclidophora, Macruriformes--l species). As regards Meta - 

 haliotrema, this genus is apparently encountered in two completely unrelated 

 families of different orders. 



Until now^, we were interested in the occurrence of the genera 

 of monogenetic trematodes on different orders of fishes; passing to the 

 analysis of occurrence on one order of fishes we will have to consider again 

 the questions concerning the interrelations of the families. 



Choricotyle, Encotyllabe, S qualonchocotyle , Pseudaxlne , 

 Heteraxine, Trochopus, Diplectanum and Haliotrema were found on four 

 and more families of fishes of one order. The first two genera are charac- 

 teristic for the suborder Percoidei and in vast majority are encountered 

 on the superfamily Percoidae; in addition to that, one species of the first 

 genus lives on representatives of a distant suborder- -Cottoidei. One must 

 note that about one-half of the species of each of the genera are encountered 

 on one family of fishes, Sparidae, which accidentally coincides for both. 

 Further, Squalonchocotyle is characteristic for five families of sharks and 

 the majority of species parasitizes Carcharhinidae and Squalidae; sharply 

 differentiated on the basis of occurrence is one species, S. t orpedinis 

 (Price) which is discovered on skates --Torpedinidae. However, the in- 

 dependence of the last species as established by Price, (Price, 1942) is not 

 altogether clear to us; it is possible that this variation (subspecies?) is 

 S. abbreviata(Olsson). Pseudaxine parasitizes practically only Scoinbroidei 

 (all five species, although one of them, in addition to that, is indicated on 

 Sparidae). For the remaining four genera the occurrence on more or less 

 related families also is characteristic, and on one or two of them in a 

 large majority of species. Thus, of the eight species of Heteraxine , five 

 are encountered on Carangidae, of 12 species of Trochopus- -nine on 

 Triglidae (one more on the more closely related family, Scorpaenidae); 

 of 12 species of Diplectanum - - 1 are found on Serranidae and Sciaenidae, 

 of 10 species of Haliotrema six occur on Mullidae and three more on 

 relatively close Percoidae. \ 



304 



