112 REPORT OF COMMISSIONER OF FISH AND FISHERIES. [406] 
cur. The Membranipora pilvsa (Plate XXXIV, figs. 262, 263) is frequent 
on rocky bottoms, growing chiefly upon Phyllophora and other alge. 
It may be known by the oval cells, bordered by erect, bristle-like pro- 
cesses, of which the one at the proximal end of the cell is much longer 
than the rest. 
Another species, J/. lineata, is also common, incrusting rocks and 
shells in broad, thin, radiating patches. In this the cells are oblong; 
crowded, and separated only by the linear margins. In the most com. 
mon variety there are eight or ten slender spinules on each side of the 
cells, which bend over so as to meet or interlock across the open cells. 
The cells are much smaller as well as narrower than those of the pre- 
ceding species. 
Of Echinoderms only a few species occur in this region, on rocky bot- 
toms, which causes this fauna to contrast very strongly with that of the 
rocky bottoms farther north, as in the Bay of Fundy or on the coast of 
Maine, where numerous other fine species of star-fishes and several addi- 
tional Holothurians are common. Thecommon green sea-urchin, Stron- 
gylocentrotus Drobachiensis, (Plate XX XV, fig. 268,) so very abundant 
farther north, and especially in the Bay of Fundy, where it occurs in 
abundance at low-water mark, and on rocky bottoms at all depths 
down to 110 fathoms, and off St. George’s Bank even down to 450 fath- 
oms, is comparatively rare in this region and chiefly confined to the 
outside colder waters, as off Gay Head and No Man’s Land, where it 
was quite common. But a few specimens were dredged at several local- 
ities in Vineyard Sound. The largest occured on the rocky bottoms off 
West Chop, and off Menemsha. It has been found occasionally in Long 
Island Sound, as off New Haven and Stratford, Connecticut, but is 
there quite rare and small. It feeds partly on diatoms and other small 
alge, &c., which it cuts from the rocks with the sharp points of its 
teeth, but it is also fond of dead fishes, which are soon devoured, bones 
and all, by it in the Bay of Fundy. In return itis swallowed whole in 
large quantities by the wolf-fish and by other large fishes.. The purple 
sea-urchin, Arbacia punctulata, is much more abundant in Vineyard 
Sound and similar waters, in this region. This is a southern species 
which is here near its northern limit. It is easily distinguished by its 
rather stout, unusually long, purple spines; by its ambulacral pores in 
two simple rows; by the upper surface of the shell being partly desti- 
tute of spines; and by the anal region, at the summit of the shell, which 
is formed of only four rather large plates. It occurred of large size, 
associated with the preceding species, off West Chop and Holmes’s 
Hole; it was quite abundant in the passage at Wood’s Hole, especially 
on shelly and gravelly bottoms north of Naushawena Island, and it was 
met with at many other localities. 
The common green star-fish, Asterias arenicola, (p. 326, Plate XX XV, 
fig. 269,) is very common on all the rocky bottoms in this region. A 
smaller and more beautiful northern star-fish was occasionally met with 
