6 PROCEEDINGS OF THE NATIONAL MUSEUM vol. 119 



both. The percentages support the conclusion that southern Cali- 

 fornia lies at the northern end of the warm-temperate province but 

 that the deep-water shelf is inhabited primarily by submergent cold- 

 temperate species. 



Presumably 16 species of table 8, marked with asterisks, represent 

 northeastern Pacific endemic boreal elements which may be found 

 throughout the Oregon province (in shallow depths in the northern 

 portion). Approximately 28 (35 percent) of the 81 known species of 

 Monterey Bay are of cold-temperate distribution. Purely tropical 

 influence is small. The remaining species are of presumed warm-tem- 

 perate affinities. 



The intertidal zone of California north of Point Conception has 

 several cold- temperate species (Barnard, MS), whereas the middepths 

 of Monterey Bay and southern California have very few, if any, of 

 these elements. These facts indicate that amphipodan distributions 

 are strongly controlled by temperature and that a wide latitude of 

 ecothermic response is possible for mud-bottom species through sub- 

 mergence because of substrate similarities between shallow and deep 

 waters. The floral substrates of intertidal waters have a narro\\ 

 range of submergence owing to the absence of illumination in deep 

 waters. Thus phycophilous Amphipoda cannot submerge to the 

 extent of their mud-bottom congeners. The thermal tolerances of 

 the cold-temperate intertidal species must therefore be greater than 

 those of mud dwellers. The temporal evolution of these intertidal 

 distributions may be favorably controlled by the occurrence of a wide 

 variety of available niches and an extensive food supply. 



Northwestern Pacific Relationships 



Only 12 of the 81 species of Monterey Bay have been found in the 

 northwestern Pacific region embracing the Japan Sea, Okhotsk Sea, 

 and Bering Sea (table 10). Two of those species, Argissa hamatipes 

 and Nicippe tumida, may be cosmopolitan in cold water. They may 

 submerge to great depths in the tropics, the former possibly occurring 

 even in shallow tropical seas. Leucothoe spinicarpa is a eurybathic 

 cosmopolite occurring in sponges. The genus Anonyx is enormously 

 diverse in the northwestern Pacific region but declines in diversity by 

 southerly increments. Only 2 species of Anonyx occur in California, 

 south of Monterey Bay. Corophium uenoi rarely occurs in the open 

 sea of California, but it is abundant in lagoons and estuaries (Newport 

 Bay, Morro Bay) and may have been introduced from Japan in 

 oyster transplants. The remaining 7 species of table 10, with the 

 exception of Ampelisca macrocephala and Paraphoxus obtusidens, are 

 scarce on the Monterey shelf. Probably they submerge or are de- 

 pleted to the south of southern California. Ampelisca macrocephala 



