455] LARVAL TREMATODES—CORT 9 



6. Distoma (Gymnocephala) ascoidca Leidy (1877:201). Host, 

 Planorbis parvus, Philadelphia, Pa. 



7. Distoma centrappendiculatum Leidy (1890:416). 

 Syn., Distoma appendicidatum Leidy (1877:202). 

 Host, Helix arbora, Philadelphia, Pa. 



8. Distoma ' comifrons Leidy (1878:382-383). Host, Donax josser, 

 Cape May, New Jersey. 



9. Distoma lasium Leidy (1890). Host, Ilyanassa obsoleta, Beach 

 Haven, New Jersey. 



10. Cercaria platyura Leidy (1890:415-416). Free in a pool at 

 Fort Bridger, Wyoming. 



11. Cercaria of Diplodiscus temporatus Stafford, Cary (1909). 

 Host, Goniobasis virginica, Princeton, New Jersey. 



The present paper adds fourteen new species of cercariae from North 

 American fresh-water snails. A preliminary report, taking up briefly 

 the structure and activity of these cercariae has already been published 

 (Cort, 1914). 



METHODS OF STUDY 



To obtain this material examinations were made of large numbers 

 of snails from various localities. I want to express my thanks to Dr. 

 Ruth Marshall, Dr. M. F. Guyer, Dr. G. R. La Rue, Dr. B. M. Allen, 

 Dr. F. W. Carpenter, Dr. H. S. Pratt, Mr. A. F. Coutant, Mr. Hermann 

 Douthitt, Dr. C. S. Mead, Dr. A. Richards, Dr. C. C. Nutting, and Dr. 

 J. E. Ackert for their kindness in collecting and shipping me living 

 snails. Without their aid it would have been impossible to have ob- 

 tained the material for this study. 



To Professor Henry B. Ward, under whose direction this work has 

 been carried on, I wish to express my appreciation for his interest and 

 helpful suggestions. 



The following method was employed in the examination of snails 

 for larval trematodes. The shell was cut or crushed so as to remove 

 the body, if possible, unbroken. An examination was then made with 

 the low power of the microscope. If larval trematodes were present, 

 some of them were almost invariably loosened from the infected part 

 and scattered around the snail in the water. The digestive gland was 

 the organ most usually infected, its color being often changed by the 

 pigmentation of the sporocysts or rediae. When infection was found 

 a part of the diseased tissue was preserved whole for sectioning, an- 



