2 3 2 ECONOMIC ZOOLOGY AND ENTOMOLOGY 



pets so common on the rocks everywhere, the helmet-shells 

 from which cameos are cut, and hosts of others all belong to 

 this group. The large sea-snails and the much smaller but 

 more numerous drills (family Muricidce) are often of serious 

 economic importance. The sea-snails bore holes by means of 

 their roughened tongue-like organ, the radula, and an acid 

 salivary secretion through even the thickest-shelled clams, and 

 suck out the soft body of the victim. The oyster-drills, of the 

 genus Urosalpinx and of other genera, drill holes through 

 the oyster shells in the same manner, and as they often occur in 

 great numbers on the oyster beds they may destroy many 

 oysters. Some of them have a habit of collecting in great 

 masses at their breeding season, and are sometimes gathered 



FIG. 107. Two kinds of oyster-drills; large one, Polynices 

 Gould; small one, Thais lamellosa. (Reduced.) 



lewis I, 



and used for food. Many Muricidce when crushed exude a 

 reddish-purple fluid which in olden times was used as a dye 

 famous under the name of Tyrian purpJe. 



Abalones, or ear-shells, which are particularly abundant 

 along certain parts of the California sea-coast, are of interest 

 because of their economic importance. The animal lives 

 attached to a rock by a great muscle which fills most of the 

 firm ear-shaped shell that covers it. The outer side of the 

 shell is rough and dull-colored but the inner surface is smooth 



