4 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [293] 
has several small chains of galvanized iron attached to the frame by 
one end, so as to drag over the bottom, and the pieces of frayed-out 
rope are attached along the sides of the chains. 
The ordinary dredges can be used on all kinds of bottom, except 
where there are rough rocks and ledges, but they generally merely 
scrape the surface or sink into the bottom but slightly. The rake- 
dredges are used only on bottoms of soft mud or sand, and are intended 
to catch burrowing animals of all kinds, which are always numerous on 
such bottoms. The trawl is adapted for the capture of bottom-fishes, 
as well as for crabs, lobsters, large shells, and all other animals of con- 
siderable size, which creep over or rest upon the bottom. It cannot be 
used where the bottom is rocky or rough, and does not usually capture 
many animals of small size, or those that burrow. It is, however, a 
very important instrument when used in connection with the ordinary 
dredge, fer it will capture those species which are too active to be 
caught by the dredge, and much greater quantities of the larger spe- 
cies than can be obtained by the dredge alone. The ‘ tangles” are 
particularly useful on rough, rocky, or ledgy bottoms, where the dredge 
and trawl cannot be used, but they cannot be depended upon for ob- 
taining al] the small species, especially of shells and worms. They 
capture mainly those kinds of animals which have rough or spiny sur- 
faces, such as star-fishes, sea-urchins, corals, bryozoa, rough crabs, &e., 
and those kinds which are disposed to cling to foreign objects, such as 
many of the small crustacea, which are often taken in countless numbers 
by this means. Star-fishes and sea-urchins are especially adapted to be 
caught by this instrument, and are often brought up in great quanti- 
ties. The tangles can be used on all kinds of bottoms, wherever there 
are any of those kinds of animals which they are adapted to capture. 
The localities where dredgings were made by these various instru- 
ments were located on Coast Survey charts as accurately as_ possible, 
and were sufficiently numerous to give a pretty satisfactory knowledge 
of the nature of the bottom and its inhabitants throughout the region 
explored. The total number of casts of the dredges made during the 
three months devoted to this work was about 400. A large part of 
these, including all the more important ones, have been located on the 
map accompanying this report. The more important points where the 
temperature of the water was observed have also been indicated on 
the map and the temperatures given, the figures above two parallel lines 
indicating the surface temperature, those below such lines indicating 
the bottom temperature—thus: $2). 
In prosecuting our explorations we soon found that there are, in the 
waters of this region, three quite distinct assemblages of animal life, 
which are dependent upon and limited by definite physical conditions of 
the waters which they inhabit. The first of these includes all those kinds 
which inhabit the bottom and shores of Vineyard Sound, Buzzard’s 
Bay, and the other similar bodies of shallow water along this coast from 
