106 



remains to be investigated in detail. It was possible to obtain some 

 quantitative figures for the nearshore sand bottom environment from eight 

 stations taken with a 1/20 m- Van Veen grab which only totaled 2 5 m-, 

 insufficient for strict square meter comparisons with other regions. An 

 average of 2.6 living individuals and 2.1 living species of animals was taken 

 from these eight samples using a 1 mm. diameter screen. Most of the 

 stations were taken in the southern Gulf, and the data for these stations 

 can be found in the appendix. The results of this survey are shown in a 

 table below. 



Station 

 Number 



1 



8 



9 

 16 

 21 

 22 

 24 

 26 



Five 1/10 m^ Petersen Grab samples were taken in one spot, within this 

 same environment, off Topolabompo near Los Mochis. Table VII gives 

 one an idea of how diverse this region is in respect to species, and also the 

 relatively low standing crop of animals which was found. These five samples 

 may offer the only valid comparison in this study with other benthic 

 studies, although the total area is still less than one half a meter. In- 

 spection of the species composition of these stations (Table VII) indicate 

 that they represent a rather good Tellina community, similar to those 

 described by Thorson (1957). Cumulative curves of these five samples, 

 as well as cumulative species curves for the eight Van Veen samples listed 

 above are given in fig. 29. These cumulative curves are based upon the 

 appearances of new species in successive samples as the area is also in- 

 creased. Fig. 29A gives first the cumulative curves for the eight samples 

 listed above in the 11 to 36 meter depth ranges, and secondly the curve 

 for equal-sized samples taken in the 1 to 10 meter depths. One can easily 

 see that the diversity is about the same in both environments. Fig. 29 b 

 gives the cumulative curve for nine nearly successive shell dredge samples 

 in the same region, also as area is increased. Both in 29 A and 29 B, plots 

 of the total number of species taken in each sample is given, in order to 

 demonstrate the relative uniformity of catch effort. Finally, in fig. 29 D, 



