172 BULLETIN OF THE BUREAU OF FISHERIES. 
end of Buzzards Bay, like its eastern shore, is comparatively free from deposits of mud, 
and accordingly we often meet with species here which occur in various parts of the 
Sound, but which are rarely or never met with in the more central parts of the Bay. 
Here again the temperature factor often leads to similar appearances, and it is therefore 
necessary to consider the total range of a species before we can form any definite con- 
clusions as to which factor is responsible in a given case. 
The scarcity or apparent total absence in Buzzards Bay of a considerable number 
of species belonging to each of the subkingdoms is, we believe, due chiefly if not entirely 
to the character of the bottom. It is true that the annual extremes of temperature are 
somewhat greater in the Bay than in the Sound, and it is true that the water density 
of the former is slightly lower; but we would attribute little importance to these factors 
in determining the differences in their respective faunas. 
Tables presented in chapter 1m show that the list of prevalent species for the 
Fish Hawk stations in Buzzards Bay is almost identical with that for muddy bottoms; 
while the list of prevalent species for the Fish Hawk stations in Vineyard Sound includes 
but two species which were not contained either in the list for sandy or in that for gravelly 
bottoms. This, however, can hardly be regarded as independent evidence that the 
differences in fauna between the two bodies of water are due to differences of the bottom. 
As regards the variety of life found to occur upon the various types of bottom, it 
was shown above that the number of species per dredge haul was greatest for the bottoms 
of gravel or stones and least for the sandy bottoms, while the muddy bottoms held an 
intermediate position in this respect. It was pointed out, however, that the greater 
wealth in species, recorded for the muddy bottoms, as compared with the sandy ones, 
might be due, in part at least, to the fact that the dredge cut more deeply into the 
former, and thus obtained a fairer representation of the burrowing organisms. 
It was likewise shown statistically that the average number of species per dredge 
haul was greater in Buzzards Bay than in Vineyard Sound. ‘This was true despite the 
fact that the total number of species encountered was much greater in the Sound than 
in the Bay. We have interpreted these facts as signifying that while the wealth of spe- 
cies is, on the average, as great or even greater at each particular point on the floor of 
Buzzards Bay, the greater diversity of conditions in Vineyard Sound as a whole results 
in its furnishing a habitat to a greater variety of species.* This conclusion is quite in 
harmony with the fact that the number of “‘prevalent’’ species for Buzzards Bay—i. e., 
the number of those taken at one-fourth or more of the dredging stations—is about the 
same (slightly greater, indeed) than the similar number for Vineyard Sound. On the 
assumption of a greater uniformity of life conditions throughout the former, a larger 
proportion of the Bay-dwelling species might be expected to occur at one-fourth or more 
of the stations, even though the total number of such species were smaller. 
We think that the reader will be impressed, as are we, by the approximate agreement 
among the figures representing the wealth in species of the different types of bottom 
distinguished by us and of the different subdivisions of the area dredged. The figures 
(p. 77) denoting the average number of species per dredge haul range from 35.2 for the 
Phalarope stations in Vineyard Sound to 39.7 for the Crab Ledge stations, the mean for 
all the stations being 37.0. Again, the lists of more ‘“‘prevalent’’ species for various 
@ See, however, discussion on pp. 79, 80, which renders this conclusion somewhat uncertain. 
