4IO FRESH-WATER BIOLOGY 



i6i (i66) Adult forms with developed sex organs. . 



162 



162 (165) Dorsal surface without special suckers. 



163 



163 (164) Anterior region flat, with foliate margins sharply set off from 

 posterior region. . . Hemistomum Diesing 1850. 



Anterior region more or less in the form of a cone opening an- 

 teriorly and ventrally. Acetabulum often covered by special ven- 

 tral holdfast organ, not larger than oral sucker, in one case entirely 

 lacking. Sexual pore dorsal. 



North American species. 



Hemistomum craterum Barker and Noll 1915. 



Length 0.7s to 1.89 mm. Cephalic region 0.62 to 0.79 mm. long 

 by 0.41 to 0.49 mm. wide. Caudal region 0.28 to 0.47 by 0.20 to 

 0.36 mm. Adhesive disk large, flattened cone with crateriform 

 top, without papillae. 



An unnamed species is recorded from Didelphis virginiana by C. 

 Curtice. 



Fig. VII. 



Hemistomum craterum. Ventral view. Magniiied. (After 

 Barker.) 



164 (163) Anterior region cup shaped, with anterior circular entrance. 



Strigea Abildgaard 1790. 



Frequently called Eoloslomum, a name of later date. 



Anterior region sharply set o3 from posterior by circular groove. Flattened lateral region 

 united ventrally to a cup, with mouth at anterior end. Concealed in this cup small acetab- 

 ulum and posterior adhesive organ in form of a papilla extending to^ mouth of cup. In genital 

 pore a well developed genital cone; opening terminal. 



North American species. 



Slrigea cornu (Rudolphi) 1819. 



Recorded from Ard^a herodias in Maryland by Stiles and Hassall. 



Another species described by Leidy as Holostomum nitidum from the small intestine of Rana 

 pipiens is according to Stafford a distome, and if so could not be placed here. 



165 (162) With row of suckers on dorsal surface. 



Polycolyle Willemoes-Suhm 1871. 



Type species. . . Polycotyle ornata Willemoes-Suhm 1871. 



Length 4.5 mm. Posterior region growing larger posteriorly, longer than anterior. In 

 mid-dorsal line 14 or 15 suckers. 



In intestine of Alligator Indus; Charleston, S. C. 



712. Polycolyle ornata. X 25- (After Willemoes-Suhm.) 



i66 (i6i) Larval forms; sex organs wanting or only partly developed. 



Sometimes difficult to separate from adults and hence noted here as well as later. 

 Compare under Holostome Cercariae, 250 (184) in this key. 



167 



