for the United States only one, C. (Tetracotyle) typica Diesing, 

 1858, is recorded for another locality than North America. 



The larval hosts are without exception mollusks. All except 

 two, Anodonta cataracta and A. marginata, are Gasteropoda. 

 Several of the species have been found in two snails, although 

 none have been recorded as infecting three or more hosts. 

 Usually where the species occurs in two hosts the infection of 

 the one is more widely spread and heavier than that of the other. 

 Several records show the parasitism of several species of cer- 

 carise within the same host species in the same locality. In fact, 

 the writer found as many as four trematode species within the 

 same host individual {Planorhis trivolvis) at DeKalb, Illinois, 

 in August, 1917. The occurrence of two cercarite species in the 

 same host individual is commonly found in the records. In this 

 case one of the parasites usually has a heavier hold on the host 

 than the other and constitutes the major infection. 



