INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 311 



containing an abunclauce of minute living animal and vegetable organ- 

 isms. In such places they grow very rapidly, and become fat and fine- 

 flavored, if not interfered with by their numerous enemies. I shall 

 have occasion to speak of the oyster again, when discussing the fauna 

 of the estuaries, &c. 



Another shell, related to the oyster and like it attached by one valve 

 to some solid object, is common, adhering to the under sides and edges 

 of rocks near low-water mark. This is the Anomia glabra, (Plate 

 XXXir, figs. 211, 212,) and it is often called -'silver-shell" or "gold- 

 shell" on account of its golden or silvery color and shining luster; and 

 sometimes "jingle-shell" from its metallic sound when rattling about on 

 the beach with pebbles, &c. This shell, however, does not grow firmly 

 to the rock like an oyster, but is attached by a sort of stem or peduncle, 

 which goes out through an opening in the side of the lower valve ; this 

 is soft and fleshy at first, but late in life often becomes ossified, or rather 

 calcified, and then forms a solid x^lug. 



Of the lower classes of Mollusca, several Ascidians and Bryozoa 

 occur under and among the rocks. Among the former the MoJgula 

 ManJiatfensis (Plate XXXIII, fig. 250) is the most common. This 

 usually has a subglobular form, especially when its tubes are con- 

 tracted, and is almost always completely covered over with foreign mat- 

 ters of all sorts, such as bits of eel-grass and sea-weeds, grains of sand, 

 &c. When these are removed its color is dark or pale olive-green, 

 and the surface is a little rough. This species is often attached to the 

 underside of rocks, but is still more frequently attached to sea- weeds 

 and eel-grass, and is sometimes so crowded as to form large clusters. 

 Another species, having some resemblance to the last when contracted, 

 is the Cynthia partita, (Plate XXXIII, fig. 246,) but besides the great 

 difference in the tubes and apertures, this has a rougher and wrinkled 

 surface and a rusty color. The specimens that grow on the under- 

 sides of stones are often much flattened, as in the figure, but it grows 

 more abundantly attached to the piles of wharves and on shell}' bot- 

 toms in shallow waters, off shore, and in such places assumt^s its more 

 normal erect position, and a somewhat cylindrical form. Each aper- 

 ture is marked with four alternating triangles of flake-white and pur- 

 plish red. This and the preceding are eaten by the tautog. Most of 

 the other ascidians are much more at home on the bottom, off shore, 

 although some of them sometimes occur at low-water on rocks or in 

 pools. 



A delicate and elegantly branched bryozoan, the Bugula tiirrlta, 

 (Plate XXXiy, figs. 258, 259,) is often found attached to sea-weeds in 

 the pools, and it is also frequently thrown up in large quantities by the 

 waves, after storms. A smaller kind, with slender, ivory-white, and 

 stellate branches, the Crisia eburnea, (Plate XXXIV, figs. 260, 261,) 

 also occurs on the sea- weeds in pools. And with this is a coarser species, 

 which forms calcareous crusts and tubercles, having the surface covered 



