[433] INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 139 
years. They afford habitations for various kinds of animals that belong 
properly on shelly or stony bottoms, such as Arbacia punctulata (p. 326,) 
Cribrella sanguinolenta, (p. 407,) and various shells, ascidians, hydroids, 
&e. The Modiolaria nigra (Plate XXX, fig. 236) was found in small 
numbers, but of good size, associated with the common muscle, in the 
deeper part of Vineyard Sound. | 
The oyster does not usually occur on true muddy bottoms in this 
region, unless placed there by human agency, but unless attacked by 
the star-fishes or other enemies they will flourish well in such localities. 
Beds of oysters on muddy bottoms always afford lodgment for large 
numbers of animals that belong properly to the shelly and rocky bot- 
toms ; these have mostly been omitted from the following list. 
Among the shells of peculiar interest that live in the mud are the 
species of Pholas. The largest and finest species, P. costata, has been 
found living in New Bedford Harbor, according to Dr. Gould. It lived 
buried in the mud two or three feet below the surface, and the speci- 
mens were dug out by the harbor-dredging machines. This is a south- 
ern species, found quite commonly on the coasts of South Carolina and 
Florida, and in the Gulf of Mexico. With the last, P. truncata (p. 372, 
Plate XX VII, fig. 200) was also obtained, but this is quite common in mud 
and peat-banks, above low-water mark. Of both the preceding species 
we dredged dead shells at Wood’s Hole and in Great Harbor, and with 
them we found fragments of another, Zirphwa crispata, which is a 
northern and European species. It is seldom that living adult speci- 
mens of such deep-burrowing shells can be obtained by the -ordinary 
dredge, and they are rarely thrown up by the waves. 
Ascidians are not often found on the muddy bottoms, and most of 
those that do oceur adhere to the shells of oysters, muscles, &c., or to 
eel-grass. Hydroids and Bryozoa are likewise nearly wanting on true 
muddy bottoms, though a few may occur on the eel-grass and oysters. 
Of Echinoderms there are but few species. The Thyone Briareus 
(p. 362) sometimes occurs where there is growing eel-grass. The common 
star-fish, Asterias arenicola, (p. 526,) has been mentioned above as in- 
habiting muscle-beds and oyster-beds. The Amphipholis abdita V.is a 
singular Ophiuran, with a small body and very long, slender, flexible, 
greenish arms, having three spines on each side arm-plate. The arms 
are sometimes six inches long. The creature buries itself deeply beneath 
the surface of the soft mud, and projects one or more of the long arms 
partially above the surface of the mud. On this account it is seldom 
dredged entire; the projecting arms are usually cut off by the dredge, 
and the animal escapes; and as it has the power of restoring lost arms, 
this is only a temporary inconvenience. The same thing probably hap- 
pens when a voracious fish seizes one of the arms, 
IL. ¥ 
