INVERTEBRATE ANIMALS OF VINEYARD SOUND, ETC. 421 



species of Udivardsia, E. Uneata Y., living in tlie interstices among 

 ascidians and the tubes of Sabella and Potamilla. 



Sponges also occur in considerable numbers. Among them the most 

 conspicuous is the Cliona sulphur ea, a bright sulphur-yellow species, grow- 

 ing into hemispherical or irregular, massive forms, of firm texture, the 

 surface covered with scattered, low, wart-like, soft prominences, about 

 an eighth of an inch in diameter, which contract when the sponge is 

 dried, leaving shallow pits. The sponge commences as a boring species, 

 on various dead shells, and as it grows it penetrates the shells in every 

 direction, forming irregular holes and galleries, which continue to grow 

 larger as more and more of the substance of the shell is absorbed, until 

 the shells are reduced to a completely honey-combed, brittle mass, or a 

 mere skeleton 5 finally the sponge begins to protrude from the surface, 

 and grows up into mammilliform masses, or small, rounded crusts, 

 which continue to grow and spread in every direction, until finally they 

 may form masses six or eight inches in diameter, with the base si)read- 

 ing over and enveloping various dead shells, pebbles, and the coral, 

 Astrangia Dance, though it often hai)pens that living specimens of the 

 latter grow upon the sponge. Owing to the remarkable boring habits 

 of this and other allied sponges, they are very important in the econ- 

 omy of the sea, for they are the principal agents in the disintegration 

 and decay of the shells that accumulate over the bottoms, thus per- 

 forming the same function in the sea that fungi and insects perform on 

 the land — the removal of dead organisms that otherwise would accu- 

 mulate in vast quantities. In this work they are aided, in most regions, 

 either by certain boring Annelids, {Dodecacerea, &c.,) or by various bor- 

 ing mollusks, {LithodomuSy PJiolas, Gastroehcena, &c.,) but the greater 

 part of this work seems to be effected by the sponges. 



Numerous species of Foraminifera were obtained on these and also on 

 the rocky bottoms, but they have not yet been studied. The most com- 

 mon kind occurs attached by one side to dead shells, algae, &c. It con- 

 sists of several chambers arranged in a spiral manner, and to the naked 

 eye resembles a minute depressed spiral shell. 



List of species inhabiting gravelly and shelly bottoms of the bays and 



sounds. 



ARTICULATA. 



Insects. 



Page. I Page. 



Chironomus halophilus 115 Muscid?e, larva 335 



Pycnogonids. 



Page. 



Phoxichilidium maxillare. 415 



Page. 



Pallene, sp 409 



