PARASITIC FLATWORMS 



377 



20 (19) Acetabula small, widely separated; pharynx equal in size to oral 

 sucker. ... P. (Polystomoides) microcotyle Stunkard 1916. 



Body 3 by 0.78 mm. Caudal suckers 

 0.28 mm. in diameter. On caudal disc one 

 pair of great hooks, 0.116 mm. long, one 

 pair of intermediate hooks, 0.06 1 mm. 

 long, and small hooks, 0.017 mm. long. 

 Genital coronet of 32 equal and similar 

 hooks. 



In mouth of Chrysemys marginata', 

 Creston, Iowa. 



FIG. 655. Polystoma microcotyle. Ventral view. 

 X 9- (After Stunkard.) 



21 (17, 18) Genital hooks more than 32 in number. 



P. (Polystomoides) megacotyle Stunkard 1916. 



Body 2.5 to 2.7 by 0.71 to 0.78 mm. 

 Genital coronet 36 to 42 equal hooks. 

 Caudal suckers large, crowded. On caudal 

 disc one pair of great hooks, 0.116 mm. 

 long, one pair of intermediate hooks, 

 0.058 mm. long, and small hooks 0.017 

 mm. long. 



From mouth cavity of Chrysemys mar- 

 ginata; Creston, Iowa. 



FIG. 656. Polystoma megacotyle. Ventral view. 

 X 12. (After Stunkard.) 



22 (16) Genital hooks unequal in length. 



P. (Polystomoides} oblongum Wright 1879. 



Up to 2.5 mm. long and 1.5 mm. wide. Caudal suckers 0.2 mm. in diameter. Large hooks 

 on caudal disc 0.15 mm. and small hooks 0.015 nun. long. Genital coronet of 32 hooks, alter- 

 nately large and small, with free end sharply curved. 



From urinary bladder of Aromochelys odoratus; Canada. 



23 (15) Great hooks of caudal disc reduced in size or absent 24 



24 (25) Genital hooks 16 in number. 



P. (Polystomoides) orbicular e Stunkard 1916. 



Length 2.7 to 3.7 mm.; width 0.9 to 

 1.2 mm. Caudal suckers 0.3 mm. in 

 diameter. On caudal disc only a single 

 minute booklet 0.016 mm. long, in the 

 base of each sucker; no large hooks. 

 Genital coronet of 16 equal and similar 

 hooks. Egg spherical, 0.21 to 0.24 mm. 

 in diameter. 



In urinary bladder of Chrysemys mar- 



FIG. 657. Polystoma orbiculare. Extended. Ventral tfnala and Pseudemys scripta; North 

 view. X 10. (After Stunkard.) Carolina, Illinois, Iowa. 



