a second pair of hooks but it lies considerably above the disc or even 

 behind it on the posterior end of the body. In an undescribed species of 

 the present genus from Sconnberomorus niphonius Cuv. and Val. from the 

 Bosphorus, a part of the samples had a second pair of hooks approximately 

 in the middle of the over-all length of the attaching disc. In the species 

 described by Chauhan (Chauhan, 1945) the second pair of hooks was located 

 somewhat above the attaching disc. One must think that during the time 

 of development the growth of the disc takes place in such a fashion that 

 both pairs of hooks are separated by the part of the body which develops 

 between them. The fact that the second pair of hooks of Pricea is 

 homologous to the normal second pair in Gastrocotyle any other genera 

 does not arouse the slightest doubt and consequently and quandry of 

 Sproston on this subject is not founded (Sproston, 1946). Something else 

 is interesting here. It is quite possible that during the development of 

 representatives of this genus and possibly also of Lithidocotyle, in which 

 we could not find the second pair of middle hooks, this pair is shed just 

 as the very posterior complex of hooks is shed in Microcotyle (see page 

 213 ). Thus, we have here very singular peculiarities in the process of 

 postembryonic development in comparison with the majority of mono- 

 genetic trematodes in which the discs are armed with clamps. As regards 

 Lithidocotyle, this genus is unusually similar to Pricea and it is quite 

 possible that later they will be united, although we repeat that we did not 

 find the second pair of middle hooks among representatives of this genus 

 even with very meticulous re -examination. 



The correlations of the genera entering into the composition 

 of Gastrocotylidae are not fully apparent. On the other hand, Gastrocotyle 

 Allopseudaxine , Chauhanea and Pseudaxine have a more primitive structure 

 of the clamps than Pricea, Pseudomicrocotyle and Lithidocotyle, and on 

 the other the asymmetry of the part of the disc of the first is undoubtedly 

 a secondary phenomenon. It is most probable that they are two lines of 

 development which have diverged rather widely and this is substantiated 

 also by the peculiarities of development of the second group. 



The genus Thoracotyle, for which the presence of a relatively 

 small number of testes and of considerable simplification of the structure 

 of the sex system is characteristic, stands somewhat apart. In all proba- 

 bility, however, it is a secondary phenomenon. The lack of the material 

 itself does not permit us to make any substantial conclusions relative to 

 this genus, but it is possible that later it will have to be excluded from the 

 present family. 



Supplement 



We did not include the genera Tagia Sproston, 1946 and Hemitagia 

 Sproston, 1946, mentioned in the preceding text (see page 254 and others into 



535 



