NO. 3541 BENTHIC AMPHIPODA — BARNARD 5 



the 20 species of Monterey Bay occurring most frequently (1-21, 

 less 3) tally 220 individuals per m^, whereas they tally 493 individuals 

 in southern California depths of 75-92 and 94-183 m. The fre- 

 quency of the 20th most abundant species in Monterey Bay is 2.4 

 individuals whereas the 20th of southern California is about 7.0 indi- 

 viduals per m^. Fifty-eight species occur on the deep shelf of Monterey but 

 more than 110 species occur in depths of 75 to 183 m in southern 

 California. Of the 110 southern California species, 12 have fre- 

 quencies of less than 0.2 individuals per m^ and 39 have less than 1.0 

 individuals. This demonstrates the influence of sampling frequency. 

 All 58 species of the Monterey deep shelf occiu* in southern 

 California except for Centromedon pavor and Protomedeia penates. In 

 shallow waters, only Eohaustorius sencillus (of 23 species not found 

 in the deep zone) is not recorded from southern California. This 

 strong relationship is a result of the extreme intermixture of northern 

 and southern elements in the fauna of southern California. Perhaps 

 the intermixtiu'e results from southward range extensions of northern 

 species inhabiting areas of upwelling. 



On the other hand, many of the Amphipoda of Monterey Bay 

 were not collected in the siu-vey of Baja California (Barnard, 1964a). 

 Thirty-seven open-sea samples were collected there, an effort compa- 

 rable to that of Monterey Bay. A comparison of Monterey Bay and 

 Baja California probably suffers the effects of small numbers of 

 samples more than would a comparison between a large and a small 

 number. The sampling stations of Baja Cahfornia were scattered 

 throughout 300 km of the coastal length and occurred in a variety 

 of environments. Approximately 113 species occur in the fauna of 

 Monterey Bay and Baja California, but only 61 species occur in 

 both areas. The remaining species are Usted in groups of northern 

 and southern species in tables 7 and 8. 



These data provide an estimate of the northern or southern affinities 

 of more than 100 of the 167 species of Amphipoda occurring on the 

 benthos of southern California. A large share of the species occurs 

 in all three areas. Records from the literatiu-e supply information 

 for some of the other Amphipoda, and a few species are assigned to 

 regions by determining the general distribution of their genera. 

 Facts and approximations are combined in a checklist of species from 

 southern California (table 9). Only those species with detectable 

 afRnities are annotated with appropriate statements. The southern 

 California fauna is estimated to be comprised of 24 percent northern 

 or cold-water species, 13 percent southern or warm-water species, 

 5 percent bathyal affinity, and 58 percent interregional or poorly 

 known distribution. Northern species occur generally in deep water, 

 southern species in shallow water, and ubiquitous species in one or 



