INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 417 



occur, and they are quite generally diffused. Many 'of them have 

 already been enumerated as occurring on rocky bottoms. The Fulgur 

 carica, (p. 355, Plate XX, fig. 124,) and the Sycotypus canaliculatus, (p. 

 355,) are found chiefly on these bottoms, and are often very abundant. 

 Over a barrel of living specimens were obtained on a single excursion. 

 The Lunatia heros, (p. 354, Plate XXIII, figs. 133-136,) though generally 

 found on the sandy bottoms, also occurred in great numbers and of 

 very large size on some of the gravelly bottoms. The pretty little 

 Natica pusilla (Plate XXIII, fig. 132) is often common on these bottoms ; 

 it is usually delicately painted with brown. 



The Grepidida fornicata (p. 355, Plate XXIII, figs. 129, 129a) was one 

 of the most abundant species, often occurring adhering to each other in 

 great clusters, the lowest ones in the group adhering in turn to dead 

 bivalve shells, pebbles, shells of living Fulgur and Sycotypus, and still 

 •more frequently to these shells when dead and occupied by the larger 

 hermit-crabs, (Fupagurus pollicaris.) The dead shells of this Grepidida 

 were often found in great accumulations, covering considerable areas 

 of bottom, and with but little admixture, either with other shells or with 

 sand and gravel. 



The Grepidula unguiformis, (p. 355, Plate XXIII, fig. 127,) though very 

 common, did not occur in such great quantities. Grucibulum striatum 

 (p. 399, Plate XXIII, figs. 125, 126) is also common, adhering to vari- 

 ous dead shells. 



The Vermetus radicula (Plate XXIV, fig. 157) is a very curious shell, 

 looking, when full grown, very much like the tube of an Annelid, such 

 as Serpula or Protula, but the inhabitant is a genuine Gastropod, and 

 has a thin, spiral, horny operculum, for closing the aperture when it 

 withdraws. When young this shell often forms a very regular, closely 

 coiled, spiral shell, looking like that of a Turritella, and sometimes does 

 not become irregular until the spire is more than an inch long, but sooner 

 or later it goes off on a tangent and becomes irregular and crooked. 

 Sometimes several of these shells interlock irregularly and thus form 

 large clusters. 



The curious and minute Gwcum pulcliellum (Plate XX1Y, fig. 158) is 

 occasionally met with in considerable numbers, though very liable to be 

 overlooked owing to its very small size. Gcecum costatum V. is of less 

 frequent occurrence, and easily distinguished by the prominent ridges 

 or ribs that run lengthwise of the shell. 



Wherever algoe occur in abundance on these bottoms, the Bittium 

 nigrum (p. 305, XXIV, fig. 154) is found in immense numbers, and it is 

 generally associated with Lacuna vincta (p. 305, Plate XXIV, fig. 139) 

 and with a few specimens of Triforis nigrocinctus, (p. 305, Plate XXIV, 

 fig. 152,) Gerithiopsis Greenii, (Plate XXIV, fig. 153,) Astyris lunata, 

 (Plate XXI, fig. 110,) Anachis avara, (Plate XXI, fig. 109,) &c. On the 

 shelly bottoms Gerithiopsis terebralis and G. Emersonii ofter occur, but 

 they are not usually common. On similar bottoms, sometimes adhering to 

 g. Mis. 61 27 



