COPEPODA 



787 



fined to a single species of fish for a host, but seem able to make 

 use of a great variety, and may even attach themselves to other 

 aquatic animals, like tadpoles. Some of them can live almost 

 equally well in both salt and fresh water. 



The following key to the species of Argulus which have been 

 described from the fresh waters of America is adapted from Wilson's 

 paper on the Argulidae. 



KEY TO NORTH AMERICAN FRESH-WATER ARGULIDAE 



1 (4, 9) Carapace lobes overlap base of abdomen 2 



2 (3) Diameter of sucking disks 0.25 mm. 



Argulus caiostomi Dana and Herrick 1837. 



Spines on antennae reduced in number, small and weak; 

 abdomen small and orbicular; found on sucker, Caloslo- 

 mus commersoni, and chub sucker, Erimyzon sucetta ob- 

 loitgus. 



Fig. 1241. Argulus catostomi. (After Wilson.) 



3 (2) Diameter of sucking disks 0.15 mm. 



Argulus americanus Wilson 1903. 

 Spines on antennae large and strong, reenforced; abdomen large and broadly cordate. Found 

 on mudfish, Amia calva. 



4 (i, 9) Carapace lobes just reach base of abdomen 5 



5 (8) Carapace orbicular, wider than long 6 



6 (7) Anal sinus narrow and slit-like. Argulus versicolor Wilson 1903, male. 



7 (6) Anal sinus broadly triangular. . Argulus maculosus Wilson 1903. 

 Anal papillae lateral; bases of antennae widely separated; found upon the muscallonge, 



Lucius masquinongy. 



8 (s) Carapace orbicular, longer than wide. 



Argulus appendiculosus Wilson 1907. 

 Found upon a sucker. 



9 (1, 4) Carapace lobes do not reach abdomen 10 



10(16) Swimming legs with flagella 11 



II (13) Carapace orbicular, wider than long 12 



