INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. o83 



dant species is generally theAstt/ris lunata, (p. 300, Plate XXI, fig. 110,) 

 which generally occurs among the small alg;v and especially on the 

 Tubularians, in countless numbers; Anachis avara (p. 30(5, Plate XXI, 

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

 Plate XXIY, lig. 154) and Triforis nigrocinchis (p. 305, Plate XXIV, fig, 

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

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

 nassa ohsoleta (p. 354, Plate XXI, fig. 113) and Trifia trivittafa (p. 354, 

 Plate XXI, fig. 112) are common, especially the former; ['rosalpinx 

 cinerea (p. 30G, Plate XXI, fig. IIG) is generally to be found at or below 

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

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

 (p. 307, Plate XXIV, fig. 14G) and other species of the genus are often 

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

 somewhat decayed. Littorlna paUiata (p. 305^ Plate XXIV, fig. 138) 

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

 high-water mark, on the piles, where there are alg;e. In the harbors, 

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

 the Alexia myosotis (Plate XXV, fig. 168) may be found on timbers and 

 piles near high-watermark, and sometimes, also, Slenea planorhis, (Plate 

 XXIV, fig. 142,) Littorinella minvta, (Plate XXIV, fig. 140,) and Bissoa 

 aculeus, (p. 306, Plate XXIV, fig. 141.) Among and feeding upon the 

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

 beautiful J'Midia pilata (Plate 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 G^S^^Si?^ gymnota, was found "^^^ 

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

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

 branchifB 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 branchiic, the lower ones much shorter than the upper ones. 

 In life the branchire 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 " bivalve-shells," we find the Teredo 

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

 fixed or fioatiug, and most of them arc 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 " shij)- 

 worm," these creatures are not at all related to the worms, but are true 

 mollusks, quite nearly allied, in many respects, to the common ''long- 

 clam" {Mya) and to the Fholas. 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, whore they wei-e formed by 



