BATHYMETRIC RANGE. 235 



The establishment of the upper limit of the normal vertical range of the 

 intermediate Medusae is of quite as much importance to the oceanographer 

 as to the zoologist, since these organisms are among the most important 

 natural buoys to show the flow of oceanic currents. In the present case 

 their apparent absence or at least great rarity in the barren area west of 

 the Humboldt Current indicates that the general west or northwest move- 

 ment of the surface waters of that portion of the south-tropical eastern 

 Pacific within the trade-wind belt, correlated with the general southeasterly 

 direction of the trades, to which attention has already been called by Afassiz 

 (: 06), does not extend downward much below the upper limit of their range, 

 but is limited to a shallow surface zone, probably not extending below 

 about 200 fathoms. Otherwise the intermediate, like the surface Medusae, 

 would be dispersed from the Current throughout the barren area. 



