INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 427 



bases. Where eel-grass or algae afford opportanities for its attachment, 

 the M. ManJiattensis (p. 311, Plate XXXIII, fig. 250) generally occurs. 



The Bryozoa are not numerous, unless where dead shells are scattered 

 over the sand for their attachment, when many of the same species that 

 inhabit shelly bottoms may occur. The only species that are frequent 

 on the true sandy bottoms are Bugula tiirrita, (Plate XXXIY, figs. 258, 

 259,) which occurs attached to eel-grass, &c., and JEscJiarella variabilis, 

 (p. 311, Plate XXXIII, fig. 256,) which incrusts dead shells or other solid 

 objects ; with the last, Memhranipora lineafa, (p. 406,} and several other 

 species may sometimes be found. 



Several species of Echinoderms inhabit the sandy bottoms. The most 

 abundant one is the "sand-dollar," UcMnarachnius parma, (p. 362, Plate 

 XXXY, fig. 267,) which occurs in immense numbers on nearly all sandy 

 bottoms, except on the most exposed shoals. Another related species, 

 Melitta tesUidinaria, was dredged two or three times in Vineyard Sound, 

 but the specimens were dead and broken. It is a very abundant species 

 south of Cape Hatteras, and may be distinguished by having five large 

 ohlong perforations near the edge. 



At least three species of Holothurians live upon the sandy bottoms. 

 The most common one is the Thyone Briareus, (p. 362,) conspicuous on 

 account of its large size and dark purplish-brown color, as well as for the 

 numerous long papillse that cover its body. It was found on a sandy bot- 

 tom off Waquoit, with the Eulima oleacea (Plate XXIY, fig. 149) adher- 

 ing to its surface, just as they occurred together on shelly bottoms, (see i3. 

 418.) The Fentamera ptilcliella, (p. 420,) also inhabits sandy bottoms, in 

 shallow water. During the past winter Mr. Yinal X. Edwards collected 

 numerous specimens of this and the preceding species on Xobsca beach, 

 after storms. They doubtless live in the sand, in shallow water, a short 

 distance off the beach. In similar situations the Caudina arenata, (p. 362,) 

 occasionally occurs, but it is apparently rare in this region. It has a thick, 

 yellowish white, harsh skin, without suckers, and its body tapers off' into 

 a slender caudal portion. The common star-fish, Asterias arenicola, 

 (p. 326, Plate XXXY, fig. 269,) is not uncommon on sandy bottoms, though 

 more abundant in rocky and shelly localities. The Opliiura olivacea 

 (p. 363) lives among the patches of eel-grass in shallow water on the 

 sandy bottoms, and travels over the surface of the sand quite rapidly 

 by means of its slender, flexible rays. 



Of Hydroids very few species ordinarily inhabit sandy bottoms, and 

 the only one that is usually met with is Sydr actinia poJycUna, (p. 328,) 

 which lives on the shells occupied by hermit-crabs. Others occasionally' 

 grow on the eel-grass or on dead shells. 



The Cliona sulphurea, (p. 421,) is the only large sponge that is com- 

 monly met with on sandy bottoms, but another bright yellow siliceous 

 sponge, forming smooth, firm, crest-like lobes and plates, occurred on 

 Edgartown beach. 



