THE ECONOMIC MOLLUSCA OF ACADIA. 
39 
is the young of the Whelk, Buccinum undatnm. From this it differs in 
the absence of the longitudinal undulations and in the shape of the 
lowest part of the free edge of the opening. As stated under the des- 
-cription of B. undatum, this in P. lapillus is more or less angular and 
never lower than the lowest point (the apex being considered the upper 
Fig. 7 .— Purpura lapillus. Natural Size. 
end of the shell) of the columella, or central pillar around which the 
whorls are wound. In B. undatum on the other hand, it is always evenly 
rounded, and always a little lower than the extremity of the columella. 
Through all its variations, it yet presents a certain individuality of its 
own not describable in words, which makes it easily recognizable when 
once the student has become familiar with it. 
The Purple-shell lives upon rocky shores between high and low- 
water marks, particularly near the latter. It rather prefers exposed 
situations and is often found on ledges exposed to the full force of the 
ocean swell. It is very voracious and attacks nearly all of the littoral 
Molluscs, into the shells of which it can easily bore an opening by means 
of its file- like tongue. One writer tells us that it can bore through the 
shell of the common Mussel in from three to five minutes, while others, 
with more show of probability say that it takes two days. Can not some 
of our teachers or students who live near the shore, throw some light 
upon such questions at this? Through the hole, not larger than a large 
pin head, the animal thrusts its proboscis, and sucks out the juices of 
its prey at its leisure. The Oyster is a favorite food, and great damage 
is done to Oyster beds by this species. In England it is considered 
“ one cf the greatest if not the most destructive of the Oyster's enemies.” 
It has been so bad at times on the English beds that sixpence per hundred 
has been paid to collectors. It also attacks species of Littorina, Limpets, 
small Naticas and its own kind. It feeds very largely upon the common 
shore Barnacles, Balanus balanoides, thrusting its proboscis between the 
opercular valves of that species. Its egg-cases, urn or vase shaped, 
smooth, about one-fourth of an inch long, of a yellow or cream color tinged 
with pink, are found attached in groups on the under sides of stones, 
and in crevices of the ledges, at low tide. The young remain in them 
until their shell is well-formed and they are able to shift for themselves. 
