INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 353 



expelled, the point Civu be again tbrust forward and the movements 

 repeated. 



Two 'species of Sipnnculoid worms are also found living in the sand 

 at low-water. The largest and most common of these is the PhascoJos- 

 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, thongh 

 more commonly abont 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-lilie. 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, ^nst described, uses its proboscis. 



Another much smaller species of the same genus occurs 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 XXIII, figs. 133-136.) This species occurs all 

 along our coast, from the Gulf of St. Lawrence to Cape Ilatteras 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 Xew 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 which it preys. The 

 foot when well expanded is concave below and lubricated by a ver}^ 

 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 

 S. Mis. Gl 23 



