[353] INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 59 
expelled, the point can be again thrust forward and the movements 
repeated. 
Two species of Sipunculoid worms are also found living in the sand 
at low-water. The largest and most common of these is the Phascolos- 
oma Gouldii, (Plate XVIII, fig. 93.) This species grows to the length of 
a foot or more, and is often nearly half an inch in diameter, though 
more commonly about a quarter of an inch. The body is round and 
constantly changing in size and shape, owing to its contractions and 
expansions ; the surface is smoothish, but longitudinally lined with mus- 
cular fibers anteriorly, and transversely wrinkled posteriorly. The in- 
tegument is firm and parchment-like. The mouth is surrounded by 
numerous short tentacles, which are partially connected together by a 
thin web, and crowded together in several circles. The color is yellow- 
ish white, grayish white, or yellowish brown. It burrows deeply in the 
sand and gravel, using its body for this purpose very much as the 
Balanoglossus, just described, uses its proboscis. . 
Another much smaller species of the same genus oceurs in sand at 
low-water, and has similar habits, but it appears to be rather uncom- 
mon and has not been satisfactorily identified. 
Comparatively few species of Mollusks naturally inhabit sandy shores, 
though the shells of many species may be found on the beaches. On 
the more exposed beaches of loose siliceous sand none but those which 
have the power of burrowing quickly and deeply beneath the surface 
can exist. We find, however, that quite a number of our species, both 
of gastropods and bivalves, possess this power in a high degree and do 
habitually live on the exposed beaches of loose sand. 
Among the Gastropods one of the largest and most conspicuous is 
the Lunatia heros, (Plate X XIII, figs. 133-136.) This species occurs all 
along our coast, from the Gulf of St. Lawrence to Cape Hatteras or be- 
yond, wherever sandy shores ‘and pure waters are to be found, and it 
even seems to prefer the outer ocean beaches, where the waves break with 
full force, for it is abundant and of very large size on the outer beaches 
of the coast of New Jersey. When in motion (Fig. 134) the white soft 
parts are protruded from the shell to a remarkable extent and spread out 
broadly on all sides, so as to nearly conceal the shell; the foot is large, flat, 
and broadly expanded, with thin edges, and by means of it the animal 
is able to burrow, like a mole, beneath the surface of the sand, both for 
protection and in search of the bivalve shells upon whichit preys. The 
foot when well expanded is concave below and lubricated by a very 
abundant secretion of mucus, and therefore, when extended beneath the 
surface of the moist sand, it acts like a great sucker, holding the animal 
in place pretty firmly by the atmospheric pressure, thus serving as a 
sort of anchor in the sand. But nevertheless large numbers of these 
mollusks are uncovered, overturned, and thrown high up on the beaches 
by the storms, especially in winter and early spring. This species, like 
many others of its tribe, drills round holes through the sides of various 
6V 
