[311] INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 17 
containing an abundance of minute living animal and vegetable organ- 
isms. In such places they grow very rapidly, and become fat and fine- 
flavored, if not interfered with by their numerous enemies. I shall 
have occasion to speak of the oyster again, when discussing the fauna 
of the estuaries, &c. 
Another shell, related to the oyster and like it attached by one valve 
to some solid object, is common, adhering tothe under sides and edges 
of rocks near low-water mark. This is the Anomia glabra, (Plate 
XXXII, figs. 241, 242,) and it is often called “silver-shell” or “ gold- 
. Shell” on account of its golden or silvery color and shining luster; and 
sometimes “ jingle-shell” from its metallic sound when rattling about on 
the beach with pebbles, &c. This shell, however, does not grow firmly 
to the rock like an oyster, but is attached by a sort of stem or peduncle, 
which goes out through an opening in the side of the lower valve; this 
is soft and fleshy at first, but late in life often becomes ossified, or rather 
calcified, and then forms a solid plug. 
Of the lower classes.of Mollusca, several Ascidians and Bryozoa 
occur under and among the rocks. Among the former the Molgula 
Manhattensis (Plate XX XIII, fig. 250) is the most common. This 
usually has a subglobular form, especially when its tubes are con- 
tracted, and is almost always completely covered over with foreign mat- 
ters of all sorts, such as bits of eel-grass and sea-weeds, grains of sand, 
&c. When these are removed its color is dark or pale olive-green, 
and the surface is a little rough. This species is often attached to the 
underside of rocks, but is still more frequently attached to sea-weeds 
and eel-grass, and is sometimes so crowded as to form large clusters. 
Another species, having some resemblance to the last when contracted, 
is the Cynthia partita, (Plate X XXIII, fig. 246,) but besides the great 
difference in the tubes and apertures, this has a rougher and wrinkled 
surface and a rusty color. The specimens that grow on the under 
sides of stones are often much flattened, as in the figure, but it grows 
more abundantly attached to the piles of wharves and on shelly bot- 
toms in shallow waters, off shore, and in such places assumes its more 
normal erect position, and a somewhat cylindrical form. Hach aper- 
ture is marked with four alternating triangles of flake-white and pur- 
plish red. This and the preceding are eaten by the tautog. Most of 
the other ascidians are much more at home on the bottom, off shore, 
although some of them sometimes occur at low-water on rocks or in 
pools. 
A delicate and elegantly branched bryozoan, the Bugula turrita, 
(Plate XXXIV, figs. 258, 259,) is often found attached to sea-weeds in 
the pools, and it is also frequently thrown up in large quantities by the 
waves, after storms. A smaller kind, with slender, ivory-white, and 
stellate branches, the Crisia eburnea, (Plate XXXIV, figs. 260, 261,) 
also occurs on the sea-weedsin pools. And with this isa coarser species, 
which forms calcareous crusts and tubercles, having the surface covered 
2V 
