406 REPORT OF COMMISSIONER OF FISH AND FISHERIES. 



cur. The Membranvpora pilvsa (Plate XXXIV, figs. 262, 263) is frequent 

 on rocky bottoms, growing chiefly upon Phyllophora and other algse. 

 It may toe known toy the oval cells, bordered toy erect, toristle-like pro- 

 cesses, of which the one at the proximal end of the cell is much longer 

 than the rest. 



Another species, M. 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. The common green sea-urchin, Stron~ 

 gylocentrotus DrobacMensis, (Plate XXXV, 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 Xo 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 Xew Haven and Stratford, Connecticut, but is 

 there quite rare and small. It feeds partly on diatoms and other small 

 algse, &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 it is 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 Xaushawena Island, and it was 

 met with at many other localities. 



The common green star-fish, Asterias arenicola, (p. 326, Plate XXXV, 

 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 



