NO. 5 BARNARD: AMPHIPODA 33 



be connected with the descent of organic materials, especially detached 

 algae, down the canyon axes. Until non-canyon slopes can be sampled, 

 these displacements must remain figmentary, but the rather restricted 

 depth distribution of these species on the coastal shelf suggest that they 

 are abnormally displaced. 



11. The shallowest nearshore basins support a large proportion of 

 eurybathic species, suggesting an association between eurybathicity and 

 tolerance to environmental stresses such as low oxygen values. Never- 

 theless, only 9 species of amphipods have been collected in the nearshore 

 basins. 



12. Deeper offshore basins with oxygen values higher than the 

 shallower nearshore basins have a more diversified amphipod fauna and 

 fewer shelf species. 



13. The bathyal amphipod fauna of southern California has little 

 connection with the local sublittoral fauna. Apparently the bathyal mem- 

 bers have been derived from cold-temperate sublittoral faunas that have 

 submerged towards the tropics. 



14. Seventy-two percent of the 109 sam.ples of the coastal canyons 

 can be divided into 4 major assemblages, based on the polychaetes Pecti- 

 naria, Heteromastus, Maldane, and Lysippe. The remaining samples 

 are not allocated either because of mixing of dominants or the absence 

 of dominants. A significant proportion of samples from deepwater (600 

 -f m), is not assignable to Petersen-type communities because of the low 

 densities of organisms, absence of clearly dominating species and the lack 

 of subdominant indicator species. The Pectinaria and Heteromastus as- 

 semblages are clearly related to each other through overlapping samples 

 and tests of minimum faunal percentages. The Pectinaria {sensu stricto) 

 samples may be further subdivided according to the presence of other 

 subdominants : Capitella, Ancistrosyllis, Chloeia, Dentalium. A sketchy 

 differentiation in a depth-sediment scheme can be demonstrated. The 

 Pectinaria-Capitella association is confined largely to coarse sediments 

 with wide depth range. The Pectinaria- Ancistrosyllis association is re- 

 stricted to finely particulate sediments of shallow water. Fine sedi- 

 ments of slightly deeper water support, in succession, the Pectinaria- 

 Dentalium and Pectinaria-Chloeia associations followed by the Maldane 

 complex. The Heteromastus association is scattered across the scheme 

 from coarse to fine sediments in depths between 400 and 550 m, and 

 below that depth the remaining samples are lumped into a Lysippe- 

 Califia-Aricidea-Terebellides group that needs further study. 



