[417] INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 123 
oceur, 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 XXILLI, 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 H 
it is usually delicately painted with brown. 
The Crepidula 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, '(Hupagurus pollicaris.) The dead shells of this Crepidula 
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 Crepidula unguiformis, (p. 355, Plate XXIII, fig. 127,) though very 
common, did not occurin such great quantities. Crucibulum striatum 
(p. 399, Plate XXITI, 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 fall 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 Ocecum pulchellum (Plate XXIV, fig. 158) is 
occasionally met with in considerable numbers, though very liable to be 
overlooked owing to its very small size. Caecum costatum V.is of less 
frequent occurrence, and easily distinguished by the prominent ridges 
or ribs that run lengthwise of the shell. 
Wherever alge occur in abundance on these bottoms, the Bittiwm 
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, Piate XXIV, 
fig. 152,) Cerithiopsis Greenti, (Plate XXIV, fig. 153,) Astyris lunata, 
(Plate XXI, fig. 110,) Anachis avara, (Plate XXT, fig. 109,) &c. On the 
shelly bottoms Cerithiopsis terebralis and C. Emersonii ofter occur, but 
they arenotusually common. Onsimilarbottoms, sometimes adhering to 
10 Vv 
