82 American Fisheries Society. 



paring the new organism with the three representative genera 

 in their various aspects of shape, type of nuclei, relation of 

 axostyles and arrangement of flagella it seems clear that its 

 generic position is in Schmidt's Octomitus. 



The assignment of the organism to the genus Octomitus cati 

 hardly be made, however, without noting the confusion that 

 exists in the use of the word. There has been a disposition to 

 replace the genus name Hexamitus, established by Dujardin 

 (1841) by the name Octomitus, on the ground that it expresses 

 more accurately the number of flagellar appendages and to set 

 off the free-living Hexamita from the parasitic forms (Prowazek, 

 1904, Dobell, 1909, Schmidt, 1920). An objection to this pro- 

 cedure has been raised with good reason by Swezy (1915). 

 Clarity in nomenclature is given, however, in another direction. 

 Moroff (1903) described an intestinal parasite of the rainbow 

 trout and gave it the name Urophagus intestinalis. From the 

 figures and descriptive matter the organism was doubtless 

 identical with Octomitus and clearly not Urophagus, a name 

 given to forms which ingested food particles through the hind 

 end of the body, an activity which MorofT admitted he never ob- 

 served. Alexeieff (1910) described similar parasites of marine 

 fishes and, accepting Moroff's name, placed them in the genus 

 Urophagus. They, also, judged by the figures and descriptions, 

 belong to the genus Octomitus. By reducing Urophagus in- 

 testinalis Morofit" to a synonym of Octomitus intestinalis truttae 

 (Schmidt 1920) the intestinal parasites of the fish in so far as 

 they have been described for the Hexamitidae now find a place 

 in the genus Octomitus. 



In assigning the name Octomitus intestinalis truttae to the 

 intestinal parasite in the rainbow and brown trout, Schmidt 

 (1930) has chosen to make it a subspecies of Octomitus intesti- 

 nalis found in the rat (Prowazek, 1904) and a synonym of Hex- 

 amitus intestinalis Dujardin found in the frog. Certain diiTer- 

 ences between Schmidt's species (14) and the one found in our 

 hatcheries (1) warrant classifying the American type as a dis- 

 tinct species. The European species shows relatively small 

 nuclei, a difference in the relation of the axostyles in both adult 

 and early cyst stages, and in the absence of grooves at the caudal 

 end where the axostyles proceed outward, as the posterior flagella. 



