INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 511 



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 on a 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 f , 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. 



AKTICULATA. 



Crustacea. 



Pao-e. 



X Libinia canaliculata 339 



Bupagurus longicarpus 313 



* Pandalus annulicornis 493 



Hippoly te pusiola 395 



Crangon vulgaris 339 



* £ Diastylis quadrispinosa. . 507 

 Phoxus Kroyeri 501 



* Mcera levis 315 



Page. 



* | Ampelisca, sp 507 



* Byblis serrata 501 



* | Ptilocheirus pinguis 507 



* % Unciola irrorata 507 



* Siphonoecetes cuspidatus. 501 



\ Epelys montosus 370 



E. trilobus 370 



Anthura brachiata 573 



