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 furpura 



P. lapiUns. 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 in the tide-pools. This rather 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 it is a cold-water animal, and 

 can only survive in open, rocky stations, it will 

 probably never pass south of New York. It is 

 The same; a <jiffi cu it to describe this well-known species 



younger speci- , ... - i i mi 



Purpura lapiiius. men. because it is so extremely variable. 1 here 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 and a 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. Near 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 

 ridges are common. 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 accusation 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, incrusted exterior, 

 a transparent colorless shelly substance. Dark and chestnut-colored 



