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PROCEEDINGS OF THE NATIONAL MUSEUM 



Table 2. — Amphipods most abundant in the atoll samples collected (Ubiquity 

 index indicates number of areas through which species are distributed, from 

 table 1; the higher the number, the more widespread the species) 



1 Cosmopolitan. 



Dominant epifaunal genera. — Disregarding both those genera in 

 table 1 known to occupy sandy and silt bottoms (such as Ampelisca, 

 Paraphoxus, etc.) and brackish water genera (Grandidierella and 

 Corojihium) and considering only those species collected from washes 

 of epifaunal materials such as algae, rocks, coral heads, it is seen that 

 8 large genera dominate tropical faunas (table 3). These dominant 

 genera are best represented in the tropics as evidenced by a count of 

 their species in the Arctic-subarctic, using two publications, Gur- 

 janova (1951) and Shoemaker (1955). Casual inspection of Antarctic 

 and subantarctic papers demonstrates the same relationships. Never- 

 theless, several of the genera, such as Hyale, Photis, and Eurystheus, 

 are better represented in the subtropics, warm-temperate and cold- 

 temperate than they are in the tropics. Probably this situation 

 prevails because subtropical to cold-temperate zoogeographic pro- 

 vinces are more isolated from each other by temperature and con- 

 tinentally controlled barriers than are either tropics or Arctic-subarctic, 

 and thus more endemism has developed. For example, the warm- 

 temperate eastern Pacific is isolated from warm-temperate Japan by 

 a deep water barrier of great magnitude and from warm-temperate 

 Europe by a continent and an ocean. On the other hand the warm- 

 tropic waters form a continuous band from Africa through Indonesia 

 to Panama but warm-temperate waters are barred from continuity by 

 continents. Cold Arctic and subarctic waters are relatively con- 

 tinuous. 



