174 BULLETIN OF THE BUREAU OF FISHERIES. 
It would be hard to characterize in any brief statement the faunal assemblages 
proper to the various types of bottom. Such assemblages have been presented in 
four illustrative cases (p. 58-62), and composite pictures, including the more charac- 
teristic species, have been given elsewhere in chapter m1. An attempt to still further 
condense these data would, we fear, result in a mere statement of platitudes. It maybe 
allowable to mention, however, that the most characteristic species found upon muddy 
bottoms were annelids and bivalve mollusks, many of which were restricted to such 
bottoms; the most characteristic species found upon bottoms of stones or gravel were 
hydroids, Bryozoa, and ascidians; while the few species which were in any real sense 
restricted to bottoms of clearsand were either burrowing species (Ovalipes, Echinarachnius, 
certain lamellibranchs), or fishes (flounders and skates) which adhered closely to the 
bottom. 
3. THE INFLUENCE OF TEMPERATURE. 
The temperature factor is, with little doubt, the controlling one in the case of many 
species belonging to several different phyla. On page 74 is given a list of species which 
were dredged predominantly or exclusively in the colder waters of the region, i. e., at 
the western end of Vineyard Sound and the mouth of Buzzards Bay. Here the summer 
temperature of the bottom water averages about 10° F. (5.6° C.) lower than in the imme- 
diate neighborhood of Woods Hole. Reference to the stated ranges of these species 
revealed the fact that in 15 out of the 20 cases they are predominantly northward-ranging 
forms, some of which, indeed, are near their southern limit of distribution. Reference 
has also been made to a number of less common forms having a similar distribution, 
but which are not included among those for which distribution charts have been pre- 
pared. ‘This large proportion of northward-ranging species among those occupying the 
colder waters of Vineyard Sound and Buzzards Bay is significant in view of the fact 
that a decided minority (23 per cent) of the species dredged by us with any frequency 
throughout the region at large are to be classed as northward-ranging, according to the 
standard employed. 
It is of interest, also, to note that a large proportion of these colder water species 
were likewise taken by us at Crab Ledge, off Chatham, where the water temperatures in 
summer are even lower than at the mouth of Vineyard Sound. At Crab Ledge and at 
certain other outlying points were also taken a considerable number of species which 
appear never to enter Vineyard Sound or Buzzards Bay at all. So far as we have 
ascertained the ranges of the species, they belong, almost without exception, to the 
“Acadian” fauna characteristic of the waters north of Cape Cod. 
Another list was presented (p. 76) of species which, though otherwise of general 
distribution throughout Vineyard Sound, and in many cases throughout Buzzards Bay 
as well, are absent from just those waters to which the northern types are restricted. 
This list was found to include none of the strictly northern types, while more than half 
of the species there included were forms which found in Cape Cod their northern limit 
of distribution. It is probable that the temperature factor is the one responsible for 
this type of distribution in some cases at least. Many of these species, it is significant 
to state, are conspicuously absent from Crab Ledge. On the other hand, it is likely that for 
some other organisms (e. g., the ascidians) the uniformly sandy condition of the bottom 
in this outer portion of Vineyard Sound and the scarcity of solid objects suitable for 
attachment render it an unfavorable habitat. 
