Squalonchocotyle abbreviata has been discovered many tinnes 

 on Acanthias acanthias (L. ) (Squalidae) and more rarely on Mustelus canis 

 (Mitch. ) (Carchahinidae) . in addition to that, Palombi (Palombi, 1949) 

 notes this species from Torpedo marmorata Risso on the basis of the data 

 of Parona and Perugia (Parona and Perugia, 1890b). In connection with 

 the last indication, one must suppose that it is faulty and actually refers 

 to another species--Sq. torpedinis Price. Thus, the species under 

 examination should be considered as encountered only on two closely 

 related families. 



Squalonchocotyle is apparently actually encountered on three 

 species of three families of sharks, two of them are very close to each 

 other- -(Carchahinidae and Sphyrinidae) and one (Hexanchidae)- -further 

 removed from the first. 



Three species of Monogenoidea occur on four species of fishes 

 and are related to two genera of different families, but of one order: 

 Heterobothrium affinis (Linton); Hexabothrium appendiculatum (Kuhn) ; 

 and Gyrodactylus parvu s Bychowsky. 



Heterobothrium affinis is known with certainty froin two species 

 of Paralichthys (Bothidae) and from two species of Atherestes (Pleuro- 

 nectidae). The consanguinous relations of these two families are obvious. 

 In addition to that, the Paltus and Paltus- like flounders apparently are p. 233 

 closer to each other than other representatives of both families (Suvorov, 

 1948). 



Hexabothrium appendiculatus is encountered on two species 

 of Scyliorhinus (Scyliorhinidae) and two species of Mustelus (Carchahinidae), 

 Both fan-lilies of hosts are related to one suborder of Scyliorhinoidei (Berg, 

 1940) and have close consanguinous relations (Suvorov, 1948). 



Gyrodactylus parvus is encountered in a number of repre- 

 sentatives of the genus Nemachilus (Cobitidae) and in addition is indicated 

 for Phoxinus brachyurus Berg (Cyprinidae). The latter is known from the 

 works of Gvozdev and his collaborators (Gvozdev, Agapova, Martehov, 

 1953), who discovered this species in a rather considerable percentage of 

 infection on the gills of Golyar (Phoxinus, nobis). Thus, G. parvus is 

 undoubtedly encountered on representatives of two related families of 

 fishes (see page 230), although its basic hosts are indisputably repre- 

 sentatives of the genus Nemachilus. 



Three species occur on three species of fishes related to two 

 genera of different families of one order- -Encotyllabe nordnnanni Diesing, 

 Trochopus tubiporus (Diesing), and Hexostoma thynni (Delaroche). 



258 



