28 U.S. NATIONAL MUSEUM BULLETIN 25 8 



6 genera of Lysianassidae, Haustoriidae, and Oedicerotidae probably 

 should not be included as "normal" inhabitants of the French rocky 

 intertidal. 



No information on individual frequency of the French species is 

 available, but it may be true, as it is in California, that the most 

 diverse genera often have those species which are most abundant in 

 individuals. Thus, the Californian intertidal is dominated by species 

 of diverse genera such as Hyale, Photis, Ampithoe, Elasmopus, Eric- 

 thonius, Eurystheus, and Ischyrocerus; only 2 poorly diverse genera, 

 Aoroides and Oligochinus, are also dominant in individuals. Several 

 diverse genera with poor numerical representation in the intertidal 

 are dismissed as being those primarily adapted to other habitats: 

 Paraphoxus, Ampelisca and Corophium. Maera and Melita are diverse 

 genera with low frequency in the Californian intertidal but the first 

 is primarily a tropical genus, the second a cold-temperate genus. In 

 California the exceptional diverse genus with infrequently occurring 

 individuals is Pontogeneia (4 species in the region). 



In order to avoid publishing long lists of species, a simple com- 

 parative index has been devised to interrelate any two faunas. The 

 index base is composed of the lesser number of species occurring in 

 the same genus in two areas. The sums of all genera are tallied. The 

 sum is 48 species for the pair of geographic areas: Atlantic France 

 and California. The smallest total number of species in the two faunas 

 is the 123 of France. The index (39%) is the percent of species in the 

 same genera of the less diverse of the two faunas. 



The Californian fauna may be compared with that of other regions 

 by the above index, as follows: Magellan 37%, Japan-Okhotsk 

 Seas 51%, Plymouth-Isle of Man 46%, Indo-Pacific tropics 60% 

 (New Zealand 62%, Australia 47%, the latter two sets of data being 

 scanty and overlapping several zoogeographic provinces). The re- 

 sulting percentages are surprisingly high; they reflect the common 

 occurrence of diverse genera in all intertidal faunas of the world 

 (table 33). Diverse genera and families are listed in table 35 with the 

 numbers of their species in each fauna. The strong relationship be- 

 tween Californian and tropical faunas is a result of the common oc- 

 currence of the genera Ampithoe, Cymadusa, Elasmopus, Eurystheus, 

 Hyale, Ischyrocerus, Lembos, Maera, Photis, and Podocerus. Generic 

 similarity to the Magellan area is reflected primarily in the large 

 numbers of species of Eurystheus and Pontogeneia. Strong relation- 

 ship to the Japan-Okhotsk region occurs in the genera Ampithoe and 

 Pontogeneia. The genera Hyale, Lysianassa, and Melita are common 

 to the faunas of the British Isles and California. 



Although the intertidal amphipodan fauna of California is strongly 

 influenced by the occurrence of tropical genera (above list plus 



