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 in 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 

 Avealth 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 



o See, however, discussion on pp. 79, 80, which renders this conclusion somewhat uncertain. 



