198 WEST AMERICAN SHELLS 
sometimes be picked up on the mudflats, at the 
time of low tide. The shell as a whole is pear- 
shaped, and ends in a long canal, to the left of 
which is a deep, funnel-shaped umbilicus. The 
spire is beautifully crowned with circles of sharp 
horns, and about the middle of the outer lip there 
is a large, pointed tooth. 
We now come to the Purples, which received 
this name not because they are of a purple color 
themselves, but because in olden times a purple 
dye was prepared from the bodies of similar mol- 
lusks. This was especially true of a small Murex, 
M. trunculus, that lives in the Mediterranean Sea, 
and the inhabitants of ancient Tyre were peculi- 
arly skilful in preparing the rich ‘‘Tyrian dye.’’ 
Most of our Purples prefer to live where they 
will get frequent changes, for they select as a home 
those rocks that are alternately left bare and then 
covered again by the tide. They are carniverous 
creatures, and like the Oyster Drill they can bore 
through the thin shells of bivalve mollusks, and 
devour the poor inhabitants. We have but a few 
species on this coast, but some of them furnish 
very numerous specimens. The 
first and most common kind is 
named Purpura saxicola, Val., the 
Rock Purple, Figure 207. Though 
the cut is larger than the average, 
still specimens are sometimes found 
that are fully as large. The shells 
differ much in details, even in speci- 
mens living near each other and it 
Fig. 207, x $ 
