334 



LOWER INVERTEBRATES. 



third species, JV. vihe.r, becomes prominent. Tlie trails of these species are common 

 on the soft mud, and frequently at the end will be found a little pellet of mud beneath 

 which the animal is hidden. All the specimens, however, do not bury 

 themselves at the retreat of the tide, as they are able to live for a con- 

 siilerable time out of water. Possibly N. ohsoleta is the more common 

 form. In this, the shell is dark brown, and ornamented by a net work 

 of reticulating lines. It does not thrive well where exposed to the ocean 

 ■em.ivi.—sassa surf, but prefers sheltered inlets, extendine; in laroe numbers into inlets 



tiii-iltitla. * . . . . r 



where the water is decidedly brackish. In size it reaches a length of 

 about nil nich. JV. trivittata is slightly smaller, and white or greenish white in color. 

 The third sjiecies, JSf. vibex, is still smaller, reaching a length of half an 

 inch, and banded with ashy white and pale red, the colors being brightest 

 in the southern forms. All of the JVassce are carnivorous, drilling holes 

 through the shell of other molluscs and then feeding on the flesh. They 

 are, however, not confined to living objects, for they will accumulate 

 in large numbers around any decaying crab or fish, and, together with fig. 41s.— A^assa 

 the amjihipods, soon devour all the fleshy portions. In Europe an 

 allied species, JV. reticulata is an enemy of the oyster beds, drilling through the shell 

 in a short time. They usually select the young ojsters, but will destroy one three 

 years old in about eight hours. 



The egg-cases of Ncissa ohsoleta are among the most common of marine objects. 

 They are placed on any solid object that is handy, dead shells and the 'sand-saucer' 

 egg masses of iV(i<ii"ca being most frequently used. The capsules are curiously fluted 

 and ridged, and are crowded together without order, each 

 attached by its own pedicel. 



Purpura and its allies are by some jdaced in the Muricidffi, 

 by others in the Buccinidse. In Purpura the aperture is 

 wide, the s]>ire short, the whorls enlarging rapidly ; the col- 

 umella is flattened, and the outer lip is toothed. Purpura 

 lupillus., a dirty white or ashen species, is common to the 

 shores of Europe and North America, thriving bettei- and 

 growing to a larger size in the old world, where specimens 

 are frequently zoned with brown. On our own coast there is much variation in 

 appearance, individuals from the rocky coasts, where they are exposed 

 to the surf, having the ribs of the shell nearly smooth, while those from 

 sheltered localities have them roughened by scale-like projections. This 

 species does not range much south of Cape Cod, but north of that bai'rier 

 it is very common. It feeds on other animals, being especially fond of 

 the acorn barnacles {Balanus balanoides) which flourish between tides. 

 The eggs are laid in small oval capsules sujiported on slender stalks, ^^aiisuiesof Pmi? 

 Each capsule contains numbers of eggs, only a few of which eventually /"'™ lapUtus, 

 hatch, the others furnishing food for those that develop. 



Pmpurapatula was one of the forms which furnished the famous Tyrian jnirple, 

 the others,belonging to the Muricidae. The anim.als were gathered in large numbers and 

 crushed, shells and all, in mortar-shaped holes in the rocks, two or three feet in depth. 

 From the bruised mass a liquid was obtained which was mixed with a small amount of 

 soda and diluted with several times its weight of sea- water. At first the fluid was yel- 

 low, but, after exposure for a time to the rays of the sun, it changed to purjile. Then the 



FiQ. Wi. — Pxi.Tpura lapiUu 



