The analysis of 23 genera of Monogenoidea reproduced in Table 

 10 show that 16, i- e. > the vast majority are actually encountered on two 

 families of fishes related to each other in varying degrees. Four genera 

 ( Axinoides, Diclidophoropsis , Murraytrema, and Thoracocotyle) are 

 erroneously indicated for this group and must be ascribed to the genera 

 which are encountered on one family of hosts (here also must be ascribed 

 the new genus Pseudomurraytrenna separated by us). Of the remaining 

 three genera, the data about the occurrence of two (Ancylodiscus and Tagia) 

 are not sufficiently authenticated and cannot be utilized and one genus 

 ( Metahaliotrema ) apparently is known with certainty from two unrelated 

 families of fishes. 



According to the literary data, thirteen genera of Monogenoidea 

 are encountered each on three families of fishes (Table 11). However, this 

 is not accurate and a detailed study of the material shows that two genera I 

 must be excluded from this list. Thus, as has already been said, the data 

 on Diplectanotrema should not be taken into consideration in the analysis of 

 the normal occurrence, not only because not everything about this genus is 

 clear but also as a result of its discovery on fishes from the New York 

 Aquarium, that is, where natural interrelations could easily be disrupted. 



The genus Diclidophora is indicated for Clupeidae on the basis 

 of the work of Koratha, (Koratha, 1955b) who described D. lintoni from 

 Brevoortia guntheri (B. gunteri, nobis). Koratha found (only, nobis) two 

 specinniens of this species on one fish. The descriptions of the author 

 arouse significant doubt in the correctness of the attribution of this species 1 

 to the genus Diclidophora. Consequently it would be erroneous to take into 

 consideration the indication on Clupeidae and the genus Diclidophora should, 

 for the time being, be considered as encountered only on two hosts of two 

 related families. 



The remaining eleven genera encountered on three families of 

 fishes are encountered apparently indisputably and eight of them on nnore 

 or less related ones. Thus,Cathariotrema (a single species) is encountered 

 on sharks which are ascribed according to Berg (1940), to the order of 

 Lamniformes ; Heterocotyle--on the skates of close families; Hexostoma, 

 Gotocotyle , and Pricea --on Scombroidei (according to Gregory), Lamello - 

 discus--on close families of Percoidae; Tetrancistrum on two families of 

 Percoidei, and Siganidae which even though they are remote from the first, 

 nevertheless they are Perciformes; Tetraonchus is encountered on more 

 remote but related groups (Salmonidae plus Thymallidae and Esocidae) 

 which are undoubtedly linked genetically according to Berg (Berg, 1936). 

 Finally, three genera have more complex interrelations with their hosts. 

 The first- -Acolpenteron- -is encountered on two related families ( Catostomi - 

 dae and Cobitidae) which are linked with the suborder Cyprinoidei and to that 

 unrelated family of Perciformes --Centrarchidae. The second genus -- 

 Heterobothrium- -consists only of two species of which one is encountered 



288 



