386 MARINE INVERTEBRATES 
and grind them up, shell and all. A garment dipped in the 
mixture and then exposed to the sun would receive a rich purple 
dye. This was the basis of the famous “Tyrian purple.” The 
process was lost, and was rediscovered many centuries later, but 
it was long ago abandoned in favor of the far superior modern 
chemical dyes. 
Genus Purpura 
P. lapillus. No one who has ever spent an observant hour among the 
rocks at low tide, on the shores of Massachusetts or Maine, has failed to 
notice the myriads of P. lapillus clinging to the barnacle-covered boul- 
ders, or slowly creeping about inthe tide-pools. Thisrather pretty little 
mollusk is a native of Great Britain, and there 
attains its greatest development and exhibits 
best its marvelous range of variation. It is 
presumed to be an immigrant in American 
waters, having found its way across the sea 
by Iceland and Greenland, and thence down 
the coast. As itis a cold-water animal, and 
can only survive in open, rocky stations, it will 
; probably never pass south of New York. Itis 
Joaten sect difficult to describe this well-known species 
ger speci- oe i ° 
Purpura lapitlus. nate because it is so extremely variable. There is 
an individuality about the species which causes 
it to be recognized at once, yet its details are elusive. It is never more 
than one anda half inches long (in the United States), and varies in color 
from white through yellow to chocolate. Often it is banded in yellow 
or brown. Nedr the only sand-beach of Bar Harbor is a colony with ver- 
milion bands. The shell varies from a smooth to an exceedingly rough 
exterior, the latter being caused by raised scales along the lines of growth, 
which make the shell even prickly to the touch. Of this latter form there 
is a large colony on Campobello Island. Numerous coarse revolving 
ridgesarecommon. The columella is flattened and smooth, and its lower 
portion is a little twisted. The anterior canal is short. P. lapillus has 
been accused of attacking clams and boring their shells, as does the pre- 
daceous Urosalpinx cinerea, but the aceusation is not well founded. Pur- 
pura is carnivorous, and no doubt destroys many young barnacles; but 
with its short and small foot it would find great difficulty in digging 
in the sand for clams. 
In Florida waters there are several purpuras, which properly belong to 
the West Indian fauna, but enjoy an extensive range. 
P. patula. This species has a rounded body-whorl, and sometimes 
a low spire, which give it much the appearance of a large limpet. Its 
back is decorated with rows of nodules in regular order, -forming a 
spiral series. The chief point of distinction is the deeply excavated 
broadened, and flattened columella-lip of salmon-color. A portion of 
the whorl itself is worn down and made smooth by being dragged over 
sharp coral rocks, revealing underneath the rough, inerusted exterior, 
a transparent colorless shelly substance. Dark and chestnut-colored 
