BOTTOM FAUNA OF THE EASTERN TROPICAL PACIFIC. 9 



as far as 90' west longitude, we remained in the Humboldt current, as we 

 could readily see from the character of the temperature serials and from 

 the amount of pelagic life we obtained from both the surface and the in- 

 termediate hauls. This current also affected the bottom fauna, which was 

 fairly rich, even as far as 800 miles from the shore, while we remained within 

 the limits of the northern current (PI. •3''). As soon as we ran outside of 

 this the character of the surface fauna changed ; it became less and less 

 abundant as we made our way to Easter Island, the western half of the 

 line from Callao becoming gradually barren. This current also affected the 

 deep-sea fauna to such an extent that towards Easter Island, at a distance 

 of 1200 to 1400 miles from the South American continent, our trawl hauls 

 were absolutely barren (PI. 3'') ; the bottom of the greater part of the line 

 was covered with manganese nodules on which were found attached a few 

 insignificant silicious sponges, an occasional ophiuran, and a few brachiopods 

 or diminutive worm tubes, tlie same bottom continuing to Sala y Gomez and 

 between there and Easter Island. 



The southern part of our line from Easter Island to the Galapagos shows 

 all the featux'es characteristic of the western part of the line from Callao to 

 Easter Island ; like the latter, as far as the 12th degree of soutliern latitude, 

 it proved comparatively barren, the bottom consisting of manganese nodules 

 to within about 250 miles of the Galapagos (PI. 3''). The pelagic and inter- 

 mediate fauna from Easter Island to 12' south latitude was very poor, and 

 the serial temperatures show that we were outside and to the westward of 

 the great Humboldt current. But near the 12th degree of southern latitude 

 a sudden change took place ; the pelagic and intermediate fauna became 

 quite abundant again and soon fully as rich as at any time in the Humboldt 

 current. There was also a marked change in the temperature of the water 

 as indicated by the serials, showing that from the 12th degree of southern 

 latitude to the Galapagos we were cutting across the western part of the 

 Humboldt current (Pis. 3", 4). 



The presence of diatoms in all parts of the Humboldt current, which we 

 crossed from south of Callao to the equator at the Galapagos and west 

 towards Clipperton, shows how far the track of a great oceanic current can 

 be traced, not only by its temperature but also by the pelagic life within or 

 near it (PI. 3). When once in the warm westerly equatorial current, the 

 diatoms disappear and the bottom samples show only surface radiolarians 

 and globigerinse. 



