[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, 

 &c. The Modiolaria nigra (Plate XXXI, 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 XXVII, 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, Zirplicca 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 occur 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 Briarem 

 (p. 362) sometimes occurs where there is growing eel-grass. The common 

 star-fish, Asterias arenicola, (p. 326,) has been mentioned above as in 

 habiting muscle-beds and oyster-beds. The Ampliipliolis 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. 

 11 V 



