388 



FRESH-WATER BIOLOGY 



6 1 (50) Oral sucker, subterminal; acetabulum divided by transverse ridge 

 into two pockets. . . Subfamily Zygocotylinae Ward. 



Differs from all other subfamilies in position of oral sucker and 

 peculiar character of acetabulum. Testis lobed; cirrus sac lack- 

 ing. 



Representative American genus. 



Zygocotyle Stunkard 1916. 



Acetabulum consists of anterior part extending dorsad and 

 anteriad into body, and posterior overhanging lip bearing on each 

 side conical projection. Posterior end of esophagus surrounded 

 by muscular bulb in which fibers are not arranged in concentric 

 lamellae as in other amphistomes. Vitellaria well developed, with 

 large follicles, in extracecal region from oral sucker to acetabulum. 

 Uterus and germ glands intracecal. Eggs numerous, o.i4- by 

 0.083 nim. 



Type species. . Zygocotyle ceratosa Stunkard r9i6. 



From intestine of Anas platyrhynchos ; Nebraska. 



Fig. 674. Zygocotyle ceratosa. Ventral view. X S. (After Stunkard.) 



62 (49) Acetabulum conspicuously ventral and usually anterior to center of 



body. Reproductive organs completely or largely posterior 

 to acetabulum. . . . 63 



63 (160) No holdfast organs present except oral and ventral suckers. No 



sharp separation between anterior region with holdfast 

 organs and posterior region with genital organs. 



Suborder Distomata . 64 



64 (159) 



65 (148) 



66 (107) 



Hermaphroditic distomes. . . . 

 Ovary anterior to testes. . 



6S 

 66 



Coils of uterus do not extend posteriad beyond testes, or at most not 

 beyond the posterior testis . 67 



Bunodera (103 in this key) and Cryptogonimus (106) are exceptions. 



67 (106) Acetabulum a single typical sucker which may be stalked or united 

 with special genital sucker but is not divided 68 



68 (los) 



69 (74) 



Not more than two testes present. 



.... 69 



Both ovary and testes dendritic; uterus limited to a restricted 

 area 70 



