INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 329 



shells, &c., in sliallovr waters, both of the sounds and estuaries. It 

 forms rather dense, pale, flexible tufts, three or four inches high, with 

 very numerous slender branches. 



Of Polyps there are several species belonging- to the actinians, or 

 "sea-anemones," and one species of genuine coral, [Astraiujia^) but the 

 latter is seldom found at low- water, though common in shallow water, 

 on rocky bottoms. The most common of the actinians is the " fringed 

 sea-anemone,'' Metridium marginatum. This may almost always be 

 found on the under sides of large stones that have sufficient space be- 

 neath, in sheltered crevices near low- water mark, and adhering to the 

 rocks along the borders of the larger tide-pools, where they are shaded 

 and protected by the overhanging sea-weeds. In full expansion this 

 species has a very graceful form. From the expanded base the body 

 rises in the form of a tall, smooth column, sometimes cylindrical, some- 

 times tapering slightly to the middle, and then enlarging to the sum- 

 mit. Toward the top the column is surrounded by a circular thickened 

 fold, above which the character of the surface suddenly changes, the 

 skin becoming thinner and translucent, so that the internal radiating 

 partitions are visible through it. This part expands upward and out- 

 ward to the margin, which is folded into numerous deep undulations or 

 frills, and everywhere covered with very numerous, fine, short, crowded 

 tentacles. The tentacles also cover the upper side of the disk, half 

 way to the mouth, but are larger and less crowded in iKoportion to the 

 distance from the margin. The mouth is oval and the lips divided into 

 numerous folds. The largest specimens are sometimes five or six inches 

 high and three or font inches across the disk. The colors are extremely 

 variable. Most frequently the sides of the body are yellowish brown 

 or orange-brown, but it may be of any shade from white, flesh-color, 

 pink, salmon, chestnut, orange, yellow, light brown, to dark umber- 

 brown ; or it may be mottled and streaked with two or more of these colors. 

 The upper part of the body and tentacles are translucent, and have 

 lighter colors, generally either white, pink, flesh-color, or pale salmon ; 

 the tentacles are also frequently banded with flake-white, and often 

 have dark tips. This species, when much irritated, throws out from 

 minute loop-holes along the sides large numbers of long, slender, white 

 threads, which are covered with microscopic stinging-organs, powerful 

 enough to defend them from the attacks of fishes and other enemies ; 

 but they do not penetrate the human skin. 



Another species, the " white-armed anemone," Sagartia leucolena^ 

 (Plate XXXYIII, fig. 281,) is also common at low- water, especiallj' on 

 the under side of large stones, and sometimes nearly buried in sand 

 and gravel. This is more elongated and slender than the last, and has 

 a smaller, simple and plain disk, with the tentacles much longer and 

 more slender, and crowded together near the margin ; the surface of 

 the body is smooth and uniform, without any thickened fold. The 

 color is usually pale salmon or flesh-color, and the skin is translucent, 



