[383] INVERTEBRATE AFIMALS OF VINEYARD SOUND, ETC. 89 



dant species is generally fheAstyris hinata, (p. 300, Plate XXI, fig. 110,) 

 which, generally occurs among the small algte and especially on the 

 Tubularians, in countless numbers; AnacMs avara (p. 300, Plate XXI, 

 tig. 109) is often found in considerable number ; Bittium nigrum (p. 305, 

 Plate XXIV, fig. 154) and Triforis nigrocinctus (p. 305, Plate XXIV, fig, 

 152) are usually common and the former often is very abundant ; Cerith- 

 iopsis Greenii (Plate XXIV, fig. 153) sometimes occurs, but is rare; Ihja- 

 nassa obsolete, (p. 354, Plate XXI, fig. 113) and Tritia trivittata (p. 354, 

 Plate XXI, fig. 112) are common, especially the former; Urosalpinx 

 cinerea (p. 300, Plate XXI, fig. 110) is generally to be found at or below 

 low- water mark on the piles and buoys; Bela plicata (Plate XXI, fig. 

 107) is sometimes met with, but is not common ; Odostomia bisuturalis 

 (p. 307, Plate XXIV, fig. 140) and other species of the genus are often 

 found near low-water mark on the piles, especially where they are 

 somewhat decayed. Littorina palUata (p. 305, Plate XX1Y, fig. 138) 

 and L. rudis (p. 305, Plate XXIY-, fig. 137) nearly always occur near 

 high-water mark, on the piles, where there are algre. In the harbors, 

 where the water is brackish, and less frequently in the purer waters, 

 the Alexia myosotis (Plate XXY, fig. 108) may be found on timbers and 

 piles near high-watermark, and sometimes, also, Skenea planorbis, (Plate 

 XXIY, fig. 142,) Littorinella minuta, (Plate XXIV, fig. 140,) and Eissoa 

 aculeuSj (p. 300, Plate XXIV, fig. 141.) Among and feeding upon the 

 Tubularians growing on the piles at and just below low-water mark, the 

 beautiful ^Eolidictpilata,(P[sitQ XXV, fig. 174) may often be found, espe 

 cially in the harbors where the water is more or less brackish. 



Another related species, apparently the Gavolin&~gymnota, was foun 

 by Professor Todd, on an old wreck in the Wood s Hole passage, but 

 differs in several points from any form that has been described. The 

 branchiae were arranged in six transverse simple rows, on each side, 

 those of the second and third longest ; in the anterior rows there were 

 four to six branchiae, the lower ones much shorter than the upper ones. 

 In life the branchiae were dark green or blackish. 



Several other Gastropods are occasionally met with in these situa 

 tions, but the species above named are about all that ordinarily occur. 



Among the Lamellibranchs, or &quot; bivalve-shells, 7 s^e find the Teredo 

 tribe, nearly all of which are peculiar to submerged wood-work, either 

 fixed or floating, and most of them are capable of doing great damage, 

 both to ships and to the timber and piles of wharves and bridges, or 

 other similar structures. Although popularly known as the &quot; ship- 

 worm,&quot; these creatures are not at all related to the worms, but are true 

 mollusks, quite nearly allied, in many respects, to the common &quot; long- 

 clam&quot; (Mi/a) and to the Pholas. Like those shells the Teredo excavates 

 its holes or burrows merely for its own protection, and not for food; but 

 the Teredo selects wood in which to form its holes, and when these have 

 been excavated it lines them with a tube of shelly material. The holes 

 are very small at the surface of the wood, where they were formed by 



id ,. &quot; 

 it 



