20 



cases the specific names of these genera have been avoided, 

 since a much more detailed study of the species is required. 



Among the ophiuriods only one, Amphipholis squamata , 

 is regarded cosmopolitan. Among the amphipods there are 

 perhaps 2 or 3 species, and among the mollusks there 

 are believed to be very few. 



Patchiness 



The patterns of patchiness known in the San Pedro 

 area (Hartman, 1955) occur also in Santa Monica Bay, 

 but are less marked. A species may be abundant and 

 conspicuous in one sample, and rare to absent in an 

 adjacent one, but its recurrence can be expected in 

 other more distant samples. These variations might be 

 explained for slight changes in the character of sediments 

 such as size of grain, varying amounts of organic content, 

 differences in nutrient values of the overlying water 

 columns, proximity to kinds of foods, incidental dispersal 

 of larvae, or other indirect causes. Differences in rates 

 and/or times of larvae and other settling stocks which 

 are necessary to replenish the beds, might effectively 

 alter the entire facies of a population. Many smaller 

 species, abounding in shallow water, are known to grow 

 rapidly and may reach maturity within a period of a few 

 weeks or months. This is especially the case for many 

 polychaetes which are numerically and productively high 

 in Santa Monica Bay. 



