NO. 3 manter: a new genus of distomes 19 



gest the genera Megasolena and Hapladena for which Manter (1935, 

 p. 438) named the subfamily Megasoleninae. The essential difference 

 is the presence of an hermaphroditic sac in the Megasoleninae. Apo- 

 creadium seems to stand almost midway between these two subfami- 

 lies. If Included in the Megasoleninae, the subfamily (and family) 

 description must be altered to include forms with neither hermaphro- 

 ditic nor cirrus sac; if included in the Anallocreadilnae the subfamily 

 must be extended to include forms with a lymphatic system. For the 

 present, the writer prefers to recognize the lymphatic vessels as of 

 fundamental significance, especially since their presence is again as- 

 sociated with pharyngeal modifications and to classify Apocreadium 

 in the Megasoleninae. 



Discussion. For many years It has been the custom to classify 

 digenetic trematodes Into three groups, the Amphlstomata, Mono- 

 stomata, and DIstomata. But it has been increasingly apparent that 

 these divisions are heterogeneous and not natural. Some monostomes 

 (e. g. the Angiodictyidae) are actually amphistomes which have lost 

 their posterior sucker. Other monostomes are evidently distomes 

 which have lost the ventral sucker. In other words, members of these 

 groups may show closer relationship to one of the other groups than 

 to members of its own group. Amphistomes are generally considered 

 as the most primitive. Little study has been made of possible rela- 

 tionship between amphistomes and distomes. Dawes (1936, p. 177) 

 remarks: "Nous savons vralment peu de chose sur les relations qui 

 existent entre les DIstomata et les Paramphlstomlda; c'est un point 

 qui est vislblement neglige par les zoologlstes." The author, however 

 (Manter, 1935), has found strong evidence of such relationship 

 exactly where It would be most expected, namely among trema- 

 todes of fish. It even seemed necessary to classify two distome genera 

 (Megasolena and Hapladena) among the Paramphlstomlda. These 

 two genera showed certain features suggesting the family Allocreadl- 

 Idae where Megasolena at least was once classified. 



Apocreadium is still more evidently allocreadiid-like. It serves to 

 link the Paramphlstomlda not only to the Allocreadildae but to the 

 Anallocreadilnae. But Apocreadium can be included In the Mega- 

 soleninae especially if the lymphatic system Is to be emphasized. 

 There Is, In fact, a fairly well graded series of forms between the 

 amphistomes such as Gyllauchen and Opistholebes through Para- 

 gyliauchen, Apocreadium and the Anallocreadilnae to the Lepo- 



