132 



California basins (probably formed during the middle Tertiary [Emery, 

 I960]) have been occupied by a northern rather than a southern migration 

 of benthic animals. The Mexican basins and slope, on the other hand, 

 seem to have been occupied by a migration to the north from the Tropics. 

 Barriers separating the northern and southern borderland exist as shallow 

 ridges cutting transversely across the slope into Baja California (Krause, 

 1961 and in press). These ridges may serve to separate the migration of 

 animals from both directions. There is also some evidence from unpub- 

 lished deep current studies that the bottom waters along the coast of Cali- 

 fornia may move in a general southern direction, thus inhibiting larval 

 transport on the bottom from south to north. A thorough study of the 

 oceanography, geology and a summary of the biology of the Southern 

 California borderland basins can be found in Emery (1960). Hartman and 

 Barnard (1958) have written a more detailed study of the faunas of the 

 somewhat shallower borderland basins, which are quite different from those 

 studied in this paper. The inner basins have very shallow sills, which severe- 

 ly limit the bottom oxygen concentrations, thus benthic invertebrates are 

 often lacking or very scarce. None of the benthic species of invertebrates 

 found by Hartman and Barnard in the inshore basins were taken in this 

 present study, even though some of their samples were taken in over 1,000 

 meters. 



An analysis of feeding types produced a predominance of deposit 

 feeders and scavengers, as should be expected at these depths. Of the 

 37 species of invertebrates identified and listed previously in the discussion 

 of the assemblages, 15 are deposit feeders, five probably scavengers, 

 14 are mobile predators, two are considered suspension feeders and one a 

 fixed predator. The feeding composition, then, is about the same as that 

 determined for the abyssal assemblage to the south. The majority of the 

 gastropods from this environment are Buccinids, which are known to have 

 direct development from egg capsules, and all but one of the lamellibranch 

 species seem to have a lecithitrophic or non-pelagic development as well. 



Summary and Conclusions 



The data obtained in this study have made it possible to describe some 

 of the major benthic invertebrate communities or assemblages on the 

 continental shelf of an unusual subtropical to tropical region and have also 

 provided information as to the composition of some deep sea assemblages. 

 Seldom before, has there been an opportunity to investigate the degree 

 of association between such a large number of species (1,150) and stations 

 (272) for such a great variety of marine environments. The existence of a 



