2 ALLAN HANCOCK PACIFIC EXPEDITIONS VOL. 22 



Santa Monica and Santa Barbara Basins (Rittenberg, Emery and Orr, 

 1955). Oxygen is lowest in nearshore basins having their sill depths 

 near the oxygen minimum level, at 500-600 meters (Emery and Ritten- 

 berg, 1952). The differences in basin topography and water masses are 

 reflected in or directly correlated with the kinds and amounts of animals 

 existing on the sediments of the separate basins. 



The uniformity of the subsill water mass in any one basin (Emery, 

 1954, fig. 2) and the isolation of the basins one from another and from 

 the abyssal plain, make the study of the benthic fauna of each basin a 

 problem of comparison, from one basin to another, from basin to compar- 

 able slope depth or similar water mass, or from basin to the surrounding 

 shelf and bank fauna, where one might expect to encounter species of 

 eurybathic character. 



The results accruing from the use of a sampling device such as the 

 orange-peel-grab, direct attention to and encourage an attempt at a 

 reconstruction of faunal groups or natural assemblages of species as they 

 exist in nature. In deeper bottoms, as in the basins, one usually finds only 

 single individuals of larger to smaller species in unit grab samples. This 

 fact, together with the evidence gained from examination of photographs, 

 indicates that individuals are widely scattered. Crinoids (Florometra) , 

 sea-whips and surface urchins are most easily identified from the photo- 

 graphs (Plates 1 and 2), where they are seen to exist infrequently. Bur- 

 rowing or sedentary animals may follow a similar pattern of wide dis- 

 persal, as indicated by the distribution of mounds or surface holes. 



The larger part of a basin, such as San Pedro or Santa Monica, may 

 be populated by a single kind of association (Phyllochaetopterus-Protis- 

 Cyclopecten), or there may be more than one, as suggested by separate 

 photographs from San Nicolas and Santa Catalina Basins. In San Nicolas 

 Basin (Plate 2, fig. 2) the photographs show in one a sea-whip and 

 urchin, in the other a crinoid fauna. It is especially in the basins that the 

 composition and extent of a population can be regarded as distinct, for 

 here are groups of living animals dispersed in a frame which is limited in 

 extent and relatively uniform for long periods of time. The abundance in 

 terms of numbers of individuals, or of kinds, can be assayed for small 

 (sample size) to large (basin size) areas. 



It has been possible to obtain fairly complete sampling of some basins 

 and enough of certain others to indicate patterns of kinds and distribu- 

 tions of organisms. Three nearshore basins are more or less completely 

 known from quantitative bottom samples and photographs; six others 

 are known through scattered sampling and photographs. The results of 

 these studies are reported below. 



