were not so we would have found some of their remnants. There is no 

 basis to doubt our interpretation of the correlation of the chitinous and 

 muscular attaching formations; consequently, also in connection with 

 Hexabothriidae, one can firmly consider that just as in Diclybothriidae P- 408 



their attaching disc is secondarily changed and appears to be derived from 

 the 8-suckered and not the 6-suckered one as is the case in Polystomatidae. 

 Taking into consideration the probability of the presence of a 10-hooked 

 larva in Hexabothriidae their attribution to Oligonchoinea and particularly 

 to Diclybothriidae cannot arouse any doubt. 



Price (Price, 1942) divides Hexabothriidae s. .str. into 2 sub- 

 families - -Rajonchocotylinae and Hexabothriinae; however, this is undoubtedly 

 erroneous, as Sproston correctly indicates (Sproston, 1946),not accepting 

 this division in her re'sume''. The differences between the two basic genera 

 of the family Rajonchocotyl e and Squalonchocotyle, are so small that to 

 give them the importance of subfamily characteristics is impossible. One 

 should especially note also the fact that the morphology of the majority of 

 the species of both genera is poorly studied and in a number of cases it is 

 judged on the basis of the analogy with the structure of species studied in 

 detail, mainly by Cerfontaine (Cerfontaine, 1896, 1900 and other works). 

 The fact that this is so is indicated even by a superficial acquaintance with 

 the literature. For instance, forms discovered on skates are attributed 

 to the genus Rajonchocotyle and it is accepted that their internal structure 

 corresponds to the typical species (R. batis Cerfontaine, R. alba, Cerfontaine 

 and others), but it is impossible to judge either from the descriptions or 

 from the drawings of the authors whether this is actually so (see for instance 

 the descriptions and drawings of R. wheri Price, 1942 and R. laevis Price, 

 1942; for the latter species Price even indicates that the vaginal openings 

 are not noticeable, to say nothing about the vaginal ducts themselves). How- 

 ever, our studies have shown that the attribution of a species to a particular 

 genus on the basis of the characteristic of parasitizing sharks or skates 

 cannot be permitted. Thus, for instance, at our disposal is a new and as yet 

 undescribed species from a number of Far Eastern skates which has a very 

 peculiar structure of the vaginal ducts, now uniting in front of the vitelline 

 duct, now not uniting, and eggs with very long filaments and little feet (Fig. 

 291). Both these characters are differential for both genera and, further- 

 more, of the subfamilies of Price and pertain either to Squalonchocotyle 

 (the vaginal ducts not uniting and eggs with filaments and little feet) or 

 Rajonchocotyle (vaginal ducts which unite). Thus, the same species which 

 is found in large quantities possesses characteristics of both genera and 

 subfamilies. For us its true generic affinity is not important at the present 

 time but what has been said expresses the danger of classification according 

 to the host and also the impossibility of separatingsubfamilies on the basis 

 of the characters accepted by Price. 



The relations of the genera within the family are not quite clear. 

 One can suppose, however, that the absence of the chitinous armature of the 



489 



