^S. dianthus.^ Tubes often three inches long and one eighth of an inch wide, the fixed end coiled and contorted, free end with circular opening; tubes often show circular ridges, marking periods of growth; operculum funnel-shaped, the exterior striated and the edge bordered with short processes; wreath of gills nearly circular and divided into two symmetrical parts; color variable. It is found in tide-pools, also on the under side of rocks at low-water mark, either solitary or congregated in masses, and ranges from Cape Cod to New Jersey. GENUS ^Spirorbis^ ^S. borealis.^ A minute calcareous tube, in a close, flat coil attached on one side; easily mistaken for a minute gasteropod shell; worm has an operculum and wreath of gills. Found on the fronds of seaweeds, on shells, etc. CLASS =GEPHYREA= This class of animals, once placed near the holothurians, belongs with the annelid worms on account of their mode of development, their structure being entirely dissimilar. They are without segments and without parapodia. The body-cavity is filled with fluid and is traversed by connective tissue and fine muscular fibers. They are subcylindrical animals which can retract the anterior end of the body. The mouth is surrounded by tentacles, or by tentacular folds, and is at the base of the proboscis. They live in fissures of rocks, in sand, mud, rock, or coral, and in deep gasteropod shells. Their distribution is general. ORDER =SIPUNCULOIDEA= GENUS ^Sipunculus^ ^S. nudus.^ The body is cylindrical, a foot or more in length when extended. It is divided into two portions. The anterior end, to the [pg186] extent of one sixth of the entire length of the worm, is capable of being withdrawn into the remainder of the body. This portion is called the /introvert/. The introvert is retracted by means of special muscles forming a sheath around the gullet and connected at the other end to the body-wall about half-way down the body. It is narrower than the rest of the body and is covered more or less closely with small horny papillæ which turn backward and overlap like scales. The rest of the body is divided into longitudinal furrows and circular markings, giving it the appearance of being divided into squares. These markings correspond to muscles which lie beneath. The introvert, when retracted, leaves at the opening a lobed and plaited fold of the integument, giving the appearance of tentacles. When the introvert is expanded there is a fringe-like funnel around the mouth. The body is covered with a horny cuticle and has an iridescent luster. The animal lives buried in the sand and feeds upon sand, deriving its nourishment from the organisms contained therein. The sipunculoids pass so much sand and mud through their bodies that they are said to modify the mineral substances on the bottom of the sea, as earthworms do the soil of the land. GENUS ^Phascolosoma^