[829| INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 35 
shells, &c., in shallow 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, (Astrangia,) 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,” JMetridium marginatum. This may almost always he 
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 bya 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 proportion 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 four 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; orit 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 XX XVIII, fig. 284,) is also common at low-water, especially 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, 
