289] NORTH AMERICAN MONOSTOMES 71 



In the above comparison the bulbous vagina of Stafford has been con- 

 strued to be the ventral sucker and considering this as a sucker this species 

 agrees in every important anatomical feature with the Heterophyidae. The 

 absence of scales here if they have not actually been overlooked could be 

 considered only of specific import and according to the findings of Ward 

 and Hirsh (1915:148) "spines and scales are caducous in life and are easily 

 lost also if the specimens lie in preserving fluid for some time. 

 ^ The fact that this species was found in the swim bladder of Amiurus 

 nebulosus is not sufficient reason for its separation from the Heterophyidae 

 since three genera of that family are known to have larval stages in fish, 

 namely, Metagonimus, Cryptocotyle, and Paracoenogonimus. Ransom 

 (1920:530) surmises that "Heterophyes," the genus to -which. Mono stomu7n 

 amiuri seems to be most closely related, "occur in their immature stages in 

 fish," the adults thus far having been found in fish eating birds and mam- 

 mals. 



Habitat: Swim bladder Host: Amiurus nebulosus 



Locality: probably near Toronto, Collector: Stafford 

 Canada 



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