NO. 14 MANTER : DIGENETIC TREMATODES OF FISHES 347 



one end, it assumes a heartlike shape tipped at varying angles. Mehlis' 

 gland large, between ovary and anterior testis. Laurer's canal very large 

 with thick walls, opening dorsally and medianly opposite the ovary. Uter- 

 us pretesticular but chiefly to the left of the ovary, becoming a straight, 

 narrow tube dorsal to acetabulum where it joins the male duct. Large 

 flask-shaped seminal receptacle to left of ovary or, more often, between 

 ovary and acetabulum. Vitelline follicles large, extending from near pos- 

 terior edge of the acetabulum to posterior end of body. (Anteriorly they 

 may almost reach mid-acetabular level.) They are lateral, dorsal, and 

 ventral to ceca and are confluent posterior to the testes. Eggs thin shelled, 

 variable in size, 87 to 102 by 48 to 65 /i, usually 92 to 100 by 50 to 60 /x. 

 Excretory pore terminal ; excretory vesicle extending to posterior tes- 

 tis where it forks into 2 tubules. The tubule on each side soon becomes 

 double. A single pair of smaller tubules extends to near the posterior end 

 of the body. Lymphatic vessels present. Four longitudinal vessels close to 

 intestinal ceca can be seen at most body levels. One pair of these vessels 

 extends dorsal to oral sucker. Anterior to the middle of the body the ves- 

 sels are inconspicuous and often cannot be seen probably because in a col- 

 lapsed state. The lymph vessels show no sign of branching. 



GENERIC DIAGNOSIS OF CHOANODERA 



Body thick, elongate, little tapering, spined, yellow orange. Forebody 

 with edges folded ventrally and converging to meet at posterior edge of 

 acetabulum. Acetabulum i/4 to % from anterior end, larger than oral 

 sucker. Prepharynx, pharynx, esophagus present; ani lacking. Genital 

 pore median. Testes tandem, close together. Seminal vesicle and prostate 

 gland free in parenchyma; cirrus sac and cirrus lacking; tubular genital 

 sinus present. Ovaiy pretesticular, to the right, ovoid, tapering toward 

 one end; seminal receptacle, Mehlis' gland, and Laurer's canal all well 

 developed. Uterus largely to left of ovaiy. Vitellaria well developed. 

 Eggs large, thin shelled. Excretory vesicle to posterior testis with 2 pairs 

 of anterior and one pair of posterior tubules. Four longitudinal, un- 

 branched lymph vessels. Type species : Choanodera caulolatili. 



The name choanodera is from choan (= funnel) and dera {^= neck), 

 and refers to the characteristic form of the forebody. 



Comparisons. Choanodera is closely related to Apocreadium Manter, 

 1937. The ventrolateral folds of the forebody give a superficial resem- 

 blance to Bianium, which genus, however, is fundamentally dififerent in 

 possessing ani and a cirrus sac, and in lacking lymph vessels. Choanodera 



