Methods of Counting and Computing the Crustacea. 435 
August 1, 1894. 
After computing the percentage for each series of observa¬ 
tions, the average distribution of each, of the species was de- 
termined for each period and for the entire month. In deter¬ 
mining these averages the total number of Crustacea obtained 
from each level was found and divided by the number of obser¬ 
vations. The sum of all these results form the base on which 
the average percentages were computed. In this way observa¬ 
tions could be used which did not form part of complete series,, 
and in several cases one or two more observations were included 
in the upper level than in some of those below. The number of 
Crustacea, however, was in general so nearly uniform that the 
inclusion or omission of these partial observations made no ap¬ 
preciable difference in the percentages. 
In determining the averages for the month a similar methods 
was used. Each series of observations was used by itself, and 
the average for the month is the average for the observations,, 
and not the average of the different periods taken as units. 
Since these periods are unequal in length they have a different 
value in determining the total average, but it seemed to us that a 
fairer average would be reached by taking the observations in, 
this way, rather than by considering each period as a unit. 
Our discussion of results is based rather on percentages of' 
distribution than on actual numbers of Crustacea per square or- 
cubic meter. This has been done for two reasons: First, the 
coefficient of the dredge was not determined at the time that 
the computations were made, and it was therefore impossible foir 
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