has two branches not forming outgrowths and merging with each other at 

 the posterior end. The male sex opening and the opening of the uterus enter 

 the common genital atrium which opens on the side of the body, ^ The 



1 



A peculiarity which, as is known, is characteristic for tapeworms. 



copulatory organ lacks chitinous armature. There are 2 testes lying 



one behind the other. The ovary is curved or rounded and lies medially 

 from both intestinal branches. The vaginal ducts apparently are absent. 



Parasites of Echeneidae and Carangidae. 



Type and only genus, Dionchus Goto, 1899. 



In the diagnosis the minimal number of septa is indicated with 

 a question mark. This is a result of our doubting the correctness of the 

 data of Goto (Goto, 1899) who describes and pictures the disc of ^ agassizi 

 Goto with 10 septa. In our relatively voluminous material from different 

 regions of the World Ocean (probably a spelling error in the Russian and 

 should be Pacific Ocean, nobis), the worms always had 14 septa and, inasmuch 

 as this corresponds to the number of edge hooks, it seems probable to us 

 that Goto committed an error in this case in not noticing the parts of weakly 

 developed septa. All the other data of this excellent researcher are sub- 

 stantiated by our material. 



Until this time Dionchus was isolated into a special subfamily 

 as far back as 1922 (Johnston and Tiegs) and was considered as a repre- 

 sentative of the family Monocotylidae, which, however, should not be con- 

 sidered correct. Thus, it differs from Monocotylidae (s. str . ) by a number 

 of very substantial characteristics. The first of them is the structure of 

 the attaching disc, which appears at first sight similar in both families. 

 However, we have indicated for Monocotylidae the presence of septa which 

 are complete, i.e., they reach the central depression and their number 

 is always such that there is a septum "of the first order" in the middle of 

 the anterior half of the disc, whereas the Dionchidae do not have the 

 middle septum and in its place lies a corresponding depression between the 

 2 anterior septa (see Fig. 16). At the same time, as is seen from the 

 diagnoses of both families, Dionchus has only 2 and not 4 hooks as in 

 Monocotylidae (s. str. ) along the posterior edge of the disc between the 

 septa in which the middle hooks lie. Besides that the number of the septa p. 373 

 in this section of the disc is different. Among Monocotylidae there is 

 either one septum or there are none, and in Dionchidae this section is 

 equipped with 2 weakly developed septa. Hence, we can conclude that the 

 similarity between the structure of the disc of both families is only of 

 general nature and on the other hand, the differences are quite important. 



444 



