[511] INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 217 
this basal membrane buds arise, which soon grow larger and become 
like the parent polyp, while the basal membrane continues to extend 
itself and new buds to develop, until the whole shell becomes incrusted 
by the membrane, inside and out, while a number of beautiful polyps 
- arise from the upper side of the shell, and turn their mouths in different 
directions. The number of the polyps in these colonies varies, accord- 
ing to the size of the shell, from three to ten or more. Finally, by some 
chemical process, the polyps, or rather their basal membranes, dissolve 
the shell entirely, and apparently absorb it into themselves. And yet 
the membranes retain the spiral form of the shell very perfectly, and the 
hermit crab eventually actually lives inside the membranes of the polyps, 
which continue to grow and even to enlarge the chamber for the use of 
the crab, so that it need not change its habitation for a larger one as it 
grows older. When fully expanded these polyps are about an inch high, 
and are capable of changing their form considerably, but they are gen- 
erally more or less cylindrical, or else hour-glass shaped. There are 38 
or more tentacles, in full grown ones, and they are subequal, long, 
slender, acute, arranged in two close circles, and usually held in a 
recurved position, (as in fig. 287,) with those of the outer circle more 
recurved than those of the inner ones; corresponding with the bases of 
the alternate tentacles there is an outer circle of triangular points or 
lobes, covered externally, like the rest of the exterior of the body, with 
adherent and imbedded grains of fine sand. The mouth is bilabiate, 
often somewhat raised ona conical protrusion of the disk, the lips many- 
lobed, or plicate. The integument of the body when fully expanded is 
translucent, pale flesh-color, or salmon-color; disk and tentacles salmon- 
color, or pale orange, sometimes white, the lips and inside of the mouth 
brighter orange. 
List of species inhabiting bottoms composed of soft mud and sandy mud off 
the outer coast. 
In the following list those species that were found on the soft, sticky 
mud, in 11 to 19 fathoms, off Gay Head, are designated by the sign {, pre- 
fixed to their names. Those that occurred at 87, a, b, in 29 fathoms, 
fine sandy mud, fifteen miles east of Block Island, are designated by an 
asterisk prefixed. 
ARTICULATA. 
Crustacea. 
Page. Page. 
{ Libinia canaliculata....... 339 | *t Ampelisca, sp...-..---- 507 
_ Kupagurus longicarpus. ..-. 313 | * Byblis serrata........... 501 
* Pandalus annulicornis..... 493 | *{ Ptilocheirus pinguis.... 507 
Hippolyte pusiola.......... 395 | * t Unciola irrorata........ 507 
Crangon vulgaris..........- 339 | * Siphoncecetes cuspidatus. 501 
*{Diastylis quadrispinosa.. 507 | { Epelys montosus.....-... 370 
Phoxus Kroyeri...---.----. 501 | E. trilobus .........-.--... 370 
* Moera levis.-.--.-...-+--. 315 | Anthura brachiata ....-.... 573 
