MOLLUSCS. 335 



wool was dipped into the dye for a few hours and taken out colored. During tlie 

 change in color a fetid odor like that of assafcetida is given off. To obtain the finest 

 color a mixture of two species of Purpura or Murex in certain i)ropoi-tions was em- 

 ployed. For a long time the art of coloring with the secretions of molluscs was 

 entirely lost, but at the close of the middle ages it was rediscovered. Modern 

 chemistry has, however, replaced it, and now the use of hkiIIusc'hi dyes is nearly or 

 i|uite extinct. 



In VoHcholepas peruviana, the only species of the genus, the body whorl increases 

 so rajiidly in size as to render the shell much like that of a lim])et. This species occurs 

 along nearly the whole of the western 

 coast of South America, and is extensively 

 eaten by the Ciiilians and Peruvians. The 

 flesh is tough, and is beaten to make it 

 more tender. The species of Rupaua 

 live upon coral reefs, feeding u])on the 

 polyps. The genus lUdzochilus is notice- 

 able from the fact that the young of one 

 species has a well-formed shell much like 

 that of Rapana; but as the adult condi- 

 tion is reached it cements to the shell, 

 branches of the coral Antipathes or other 



, ,, . , ., , 1 11 Fig. 421. — Jihizochilusanfipatharum, fastenedtohrSinchQa 



shells, or both, until at length all means of .^nW^jaMes ,■ on the right a young specimen. 



of communication with the exterior is by 



means of the siphonal canal, the aperture being completely closed. What is the cause 

 of this peculiar self-immurement no one has yet been able to decide. Other species of 

 the genus are not known to possess such habits as those just described of JR. antipath- 

 arum. In R. maclreporariuiu the animal attaches itself to the larger reef-building 

 corals by means of the foot. 



Another interesting genus is 3Iaf/ilus, the sj)ecies of which all belong to the east- 

 ern seas. It is a fine example of that degeneracy which occurs in certain molluscs. 

 The young Magilus begins life as a well-behaved mollusc with a i-egular spiral shell ; 

 but shortly it settles down on some growing coral, and then a race begins between the 

 two slow-growing forms. If Magilus kept quiet and grew no further, a short time 

 would suffice to comj)letely envelop him in the stony coral ; but, as soon as he is par- 

 tially covered, the whorls of the shell leave their spiral course, and grow out as an 

 irregular tube. As the coral groA^'s, new additions are made to the shell, and the 

 neck-and-neck race is kept uji until the mollusc or the coral dies. Soon the tube 

 becomes too long foi- tlie mollusc, and he leaves the spiral portion and comes out to 

 live in the outer straight tube, filling up the deserted whorls with a solid deposit of 

 lime. 



In the CoLUMBELLiD^ the shell is oval, the spire moderately short, the aperture 

 narrow, and terminated by a very short anterior canal ; the outer lip is thick and 

 internally crenulated, while the columellar lip is toothed. The species are mostly 

 small, and many are briglitly colored. On our eastern coasts several species occur, 

 among thtm Colunibdla avara, lunata, ornata, etc., while on the west shores the genus 

 is represented by four species. In the tro])ics the number is much larger, some three 

 hundred being known from the whole world. All are littoral, carnivorous forms, 

 abundant on seaweeds and hydroids, and in jiools left by the retreating tides. 



