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number of species there as in the southern Gulf. Small trawl samples were 

 also taken in the southern section of this environment, and if anything, 

 the diversity of species was even greater than that produced by the shell 

 dredge. Although the species are not listed for the above two grab sample 

 stations, only one species was taken more than once, equalling the diversity 

 found in the grab sample survey of the shallow, sand-flat environment. 

 Either invertebrate distribution is extremely patchy on the continental 

 shelf of the Gulf of California, or each population of species is spread very 

 thinly over the bottom. Since the species composition is fairly similar in 

 the nine stations cited above, the latter alternative is probably the correct 

 one. Certainly, there is no apparent dominance of macro-invertebrate 

 species indicated here, similar to the boreal region studied by Petersen 

 (1911-1915), Thorson (1957) or Sanders (1956 and 1960) although such 

 a small bottom area was sampled quantitatively that valid comparisons 

 are impossible. Animals of the size studied by Sanders were not identified 

 in this study, although everything was saved which could be retained in 

 1 mm. screens. It was observed that relatively few polychaetes, amphipods 

 or copepods were collected from these sediment samples. This same lack 

 of dominance of any one species of invertebrate, large or small, was also 

 observed on the fine sandy bottoms of the northern Gulf of Mexico (Par- 

 ker, 1956a and 1960). Few quantitative benthic invertebrate studies have 

 been undertaken in the tropics and sub-tropics, with the exception of 

 Thorson's (1957 and personal communication) in the Persian Gulf (which 

 being hypersaline and very hot is on the whole a rigorous and unfavorable 

 environment), Buchanan's (1958) off Ghana, and Longhurst's (1957 and 

 1958) off Sierra Leone, Africa. For this reason it is difficult to make com- 

 parisons of standing crop and species diversity between the tropics and 

 the more well-known boreal regions. Sparck (1931) discussed the quan- 

 titative aspect of benthic populations as deduced from a small number of 

 samples in the Mediterranean. Although the waters sampled for this study 

 are generally warm, some of the species taken may also occur in Boreal 

 regions. Only a few very abundant species occurred in these samples, 

 paralleling the Danish communities of Petersen (1911-1915). Although 

 there seems to be no dominance of particular species of invertebrates in 

 the American sub-tropical regions, there is certainly dominance in the 

 Gold Coast area of West Africa (Buchanan, 1958) and off Sierra Leone 

 to the north (Longhurst, 1957 and 1958). In each of Buchanan's five 

 communities, lying roughly parallel to each other in descending depth, 

 there are about ten moderately abundant species, and at least one or two 

 very abundant species of invertebrates. No mention was made of the 



