[361] INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 67 
ward motion is obtained. It is a singular sight to see this shell swim 
swiftly many times around a vessel of water, at the surface, until, 
finally, becoming exhausted by its violent exertions, it sinks to the 
bottom for rest. 
The common “scollop,” Pecten irradians, (Plate XXXII, fig. 243,) is 
also frequently found living on sandy shores and flats, or in the pools, 
but it belongs more properly to the sheltered waters of the ponds and 
estuaries, where it lives among the eel-grass. It will, therefore, be 
mentioned again in that connection. 
The “common muscle,” Mytilus edulis, (p. 307,) is frequently found in 
large patches on sandy flats, fastened together by the threads of 
byssus. Some of the most beautifully colored varieties, (fig. 234,) with 
radiating bands of blue and yellow, are often found in such places, but 
the species is much more abundant and larger in other situations, 
especially in the shallow and sheltered waters of the bays, where there 
_is more or less mud. 
Ascidians are almost entirely wanting on the sandy shores, but Mol- 
gula Manhattensis (p. 311, Plate XX XIII, fig. 250) is sometimes found 
even on sandy shores, attached to eel-grass. 
Of Bryozoa only two species are usually met with, and even these do 
not have their true stations on the sandy shores. The delicate and 
gracefully branched Bugula turrita (p. 311, Plate XXXIV, figs. 258, 
259) is occasionally found growing attached to the eel-grass, which 
often grows in the sandy tide-pools, or at extreme low-water. It also 
occurs in great abundance among the masses of sea-weeds thrown up 
by the waves on the sandy beaches. Such specimens are often large 
and luxuriant, in some cases being more than a foot in length ; these 
are derived from the bottom in deeper water, off shore. 
The Escharella variabilis (p. 312, Plate XX XIII, fig. 256) is often found 
encrusting dead shells of various kinds, especially such as are inhab- 
ited by the larger “hermit-crabs.” It is also cast up in abundance, on 
some beaches, from deeper water. 
The Radiates are not numerous on sandy shores, yet several interest- 
ing species may be found. Among the Echinoderms we find four 
species of holothurians, one sea-urchin, one star-fish, and one ophiuran, 
The most common holothurian is the Leptosynapta Girardii, (Plate 
XXXV, figs. 265,266.) This is along, slender, very delicate and fragile 
species, which burrows deeply in the sand or gravel near low-water 
mark. The holes are round and go down almost perpendicularly ; 
they are usually not more than a quarter of an inch in diameter. The 
creature is not quick in its motions, and can usually be found in the 
upper part of its burrow when the tide is out. The skin is thin and 
quite translucent, so that the white muscular bands that run lengthwise 
of the body, on the inside, can be easily seen, as well as the large intes- 
tine, which is always quite full of sand and gives a dark appearance to 
the body. The tentacles are almost always in motion, and are used in 
