By T. HAEVEY JOHNSTON AND 0. W. TIEGS: 95 



however not altered till Liihe (1909) reintroduced that of Creplin. In 1889 

 Parona and Perugia added Wagoner's Daetylogyrus echeneis to Diplectanum. 



In 1910 Wegener removed T. monenteron from Tetra-onchus, owing mainly 

 to the character of its intestine, proposing for its reception a new genus, Mono- 

 coelium. Of the three original species of Tetraonchus, T. cruciatus is now de- 

 finitely placed under Ancyrocephalus; T. unguieulatus is identical with A. para- 

 doxus of Creplin; hence, as suggested by Stiles and Hassall (1908, p. 370), T. 

 monenteron becomes by elimination the type of the genus Tetraonchus, Wegener's 

 name {Monocoelium) being a synonym. 



The remaining species listed under Tetraonchus and Diplectanum belong 

 to Ancyrocephalus. 



Liihe uses the latter term in a wide sense to include both Tetraonchus (of 

 authors) and Monocoelium. 



MacCaUum (1915, 1917) described a number of new species of Diplectanum 

 which he regarded as a subgenus of Tetraonchus, i.e. Ancyrocephalus. Monti- 

 celli (1903) on the other hand, actually proposed a new subf ami ly, Diplectaninwe, 

 for the reception of the genus, regarding it as quite distinct from his Tetraon- 

 chinae. 



So far as we have been able to observe from the available published ac- 

 counts of MacCallum and of the earlier workers, no anatomical distinction of 

 generic value can be recognised amongst the vai-ious species included under 

 An-cyrocephalus and Diplectanum. 



The genus Ancyrocephalus, as defined above, would include A. paradoxus 

 Creplin, 1839; A. cruciatus (Wedl., 1857) Liihe, 1909; A. vanbenedenii (Par. 

 and Per., 1890) J. and T., 1922; A. aequans (Wag., 1857) J. and T., 1922; A. 

 echeneis (Wag., 1857) J. and T., 1922; A. pedatus (Wag., 1857) J. and T., 1922; 

 A. seiaenae (Ben. and Hesse, 1863) J. and T., 1922; A. teuthis (MacCallum, 

 1915) J. and T., 1922; A. lactophrys (MacCallum, 1915) J. and T., 1922; A. 

 balistes (MacCallum, 1915) J. and T., 1922; .4. longiphallus (MacCallum, 1915) 

 J. and T., 1922; A. tylosuri (MacCallum, 1917) J. and T., 1922. 

 7. Subgenus a. Dactylodiscus Olsson, 1893. 



Small Tetraonchinae in which the disc is connected to body by a long petiole, 

 and is produced laterally into a number of finger-like processes. Minor hooks 

 apparently absent. Four eyes present; intestine probably bifurcated. Testis 

 and ovary solid and near the middle of the animal. Large unlobed vesicula 

 seminalis. Penis apparently simple. Opening of oviduct probably provided 

 with booklets. Anterior fifth of worm devoid of vitellaria. 



Olsson did not mention the characters of the genus vei-y fuUy, nor did he 

 indicate whether a vagina was present. The above diagnosis is based on his 

 figures and description of the type species. 



The accentuated constriction of the disc from the body, a condition which is 

 already evident in Ancyrocephalus tylosuri (MacCaUum, 1917), and the irregular 

 lobes of the disc, an indication of which is seen in the same species, are charac- 

 ters which are scarcely of generic value. A careful determination of the pre- 

 sence or absence of the vagina would be of much greater value. The form, 

 however, probably deserves to rank as a subgenus of Ancyrocephalus. Monticelli 

 (1903, p. 336; 1905, p. 79) quoted Olsson's genus as a synonym of Tetraonchus, 



From the gills of Thymallus vulgaris and Coregonus lavaretus. 



Type species, Ancyrocephalus (Dactylodiscus) borealis Olsson. Kjiown 

 only from Sweden. 



