in the wide degree, but also, in the case ■where the monogenetic trematodes 

 are encountered on several families of fishes, in what relations the families p^ 271 

 of hosts are among themselves. Thus, eight of the 13 indicated families of 

 Monogenoidea are subject to discussion from this point of view, namely: 

 Chimaericolidae, Diclybothriidae, Hexabothriidae, Hexostomatidae, 

 Microbothriidae, Protoniicrocotylldae, Plectanocotylidae and Tetraonchidae. 



Chimaericolidae are discovered on two close families --Chimae- 

 ridae and Calliorhynchidae. Acipenseridae and Polyodontidae- -hosts of 

 Diclybothriidae, are very close to each other (Berg, 1940. ). 



Hexabothriidae are encountered on six families of sharks and 

 on three of skates, and on the first there are only representatives of Hexa- 

 bothriinae and on the second- -Rajonchocotylinae, in the scope accepted by 

 Price (Price, 1942). The exception is formed by Squalonchocotyle torpedinis 

 (Price) which are related to the first subfamily but encountered on skates of 

 the family Torpedinidae. Hexabothriidae are widely distributed on sharks; 

 thus, they are discovered on Carcharinidae (15 species of worms), 

 Sphyrnidae (6-5 species), Orectolobidae (1 species), Scyliorhinidae (2-1 

 species), Squalidae (10-8 species), and Hexanchidae (1-0 species). It is 

 more probable that subsequent research will show that representatives of 

 the family parasitize all sharks without exception. As regards the skates, 

 the Hexabothriidae, if one should set aside S. torpedinis, are discovered 

 mainly on Rajidae (12 species) and are encountered once on Rhinobatldae ; 

 further study of this group will show how normal this is. We have already 

 spoken on several occasions about the consanguinous relations between 

 sharks and skates. 



Hexostomatidae are indicated from Thunnidae, Cybiidae and 

 Carangidae. Inasmuch as the family contains only one genus, that which 

 has been said about consanguinous relations of the hosts on pag.-= 256 can 

 be also applied wholly to the family. 



Microbothriidae are encountered on four families of sharks -- 

 Squalidae (2 species of one genus of Microbothriidae), Carcharhinidae (1 

 species common with Squalidae, and in addition 2 species of two genera), 

 Scyliorhinidae (2 species of two genera), and Squatinidae (1 species). 



The consanguinous relations of all sharks are well known to 

 everyone-, however, the first and the last family are somewhat removed 

 from the two others which are more closely connected to each other 

 (S. Suvorov, 1948). In this connection, the finding of the same species on 

 Squalidae and Carcharhinidae is an important discovery which points to the 

 presence among them of a certain physiological proximity. 



309 



