Biological Survey — Erie-Niagara Watershed 



71 



depth. Positively this zone is characterized by a single species, 

 the cladoceran Latona setifera which was captured in the Helgo- 

 land trawl and is not found anywhere in the shallower water. 

 Negatively it is characterized by the entire absence of most of 

 the species peculiar to the other zones. The numerical propor- 

 tions of the various species are also very different from those 

 which prevail in the other zones. During the present survey this 

 zone was covered bv the Shearwater, belonging to the U. S. Bureau 



Surface meter and foot plankton nets 



of Fisheries, which made 6 trips in August and September, 4 

 with the meter nets and 2 with the Helgoland trawl. As 

 previously stated the bulk of the plankton in the littoral zone is 

 made up of 2 copepods and 2 cladocerans, but in the present zone 

 at least 5 copepods and 5 cladocerans have a considerable^ share 

 in the total bulk. As would be naturally expected there is also 

 here a much greater difference in the hauls made at the surface 

 and those near the bottom. This is chiefly due to an active migra- 



