GEOGRAPHICAL DISTRIBUTION. 223 



to the fact, already mentioned by Agassiz (: 06, p. x), that unfavorable 

 weather prevented making many hauls on this line. Though none of the 

 species was lacking in the barren area, yet all occurred more regularly in 

 the Current. The difference in mass of individuals of the various species, 

 taken within and outside the Current, was quite as striking in the case of 

 the Medusae as of other pelagic organisms. While within its sweep Liriope, 

 Rhopalonema, and Cytaeis occurred in swarms on several occasions, and while 

 the nets invariably yielded many specimens of other species of Medusae, 

 ctenophores, and siphonophores, to the westward of the Current but few 

 living Medusae were taken, the hauls containing, instead of perhaps several 

 hundred individuals, not more than five or ten specimens of living acalephs 

 of all kinds. On the other hand, in the barren area considerable numbers 

 of dead Medusae as well as dead animal detritus of other kinds were taken 

 (A. Agassiz, : 06). 



This decrease, though most sudden along the zone indicated by the serial 

 temperatures as the margin of the Current, progressed steadily to the west- 

 ward, the region surrounding Easter Island being the poorest. Indeed in 

 this neighborhood several successive surface hauls yielded no Medusae at 

 all, something that did not happen elsewhere during the Expedition. 



The intermediate Medusae show the same quantitative decrease from east 

 to west as do the surface species, but in much more extreme fashion. On 

 the chart, Plate 48, is represented the occurrence of six of the commoner 

 species : — Halicreas papillosum, Atolla wyvillei, Periphylla hyaciuthina, Crossoia 

 brunnea, Colobonema typicum, and Ptychogena erythrogonon. To these Nausitho'e 

 rubra, Homoenema alba, and Aeginura grimalolii might be added without 

 altering the general import. Although none of these intermediate species 

 were taken so regularly as were several of the surface forms, yet all, 

 except Ptychogena erythrogonon which was restricted to the neighborhood 

 of the Peruvian coast, occurred frequently on all our lines so long as we 

 were within the sweep of the Current, both in its north and south course 

 and in its westward extension ; but, as is shown on the chart, there is no 

 record of a single individual of any of these species in the barren area to 

 the westward of the fairly well-defined outer limit of the Current. This 

 lack is especially striking in the case of Halicreas papillosum, inasmuch as 

 this species, in the regularity of its occurrence, occupies among the inter- 

 mediate forms the same position that Liriope tetraphylla and Ehopalonema 

 velatum do among the surface species. We have no right, however, to 



