304
THE ESSEX NATURALIST.
two days to bore through a moderate sized mussel, a period
comparable with that required by Urosalpinx and Ocinebra
to bore through an oyster shell.
This tingle has been observed to attack oysters but, unlike
Urosalpinx and Ocinebra, it is doubtful if it ever feeds mainly on
oysters, even when it occurs on oyster beds. Definite experi-
ments on selective feeding in this animal would probably yield
interesting facts.
Very fine specimens of Purpura lapillus occur on the Whit-
stable oyster beds and fine specimens are not infrequent on the
beds in the River Blackwater. The chief food of Purpura un-
doubtedly varies in different habitats. Where mussels (Mytilus
edulis) are common on a rocky foreshore, these with Balanus
balanoides form the main food. Where mussels are absent on
such a shore, B. balanoides is usually the main source of food, but
in certain places, as at Hannafore Point, Looe, various Gastropods
are attacked in unusual numbers. On one day I collected at Looe
at random 1,000 shells of dead Patella vulgata at the high water
line and found that nearly 50 per cent. had been bored at least
once, and with little doubt all by Purpura. On another occasion
(May 2, 1914) during a short search I took 45 Purpura in the
act of boring into living Gastropods (mostly Littorina littorea,
Gibbula cineraria and umbilicata and Monodonta crassa) which
were generally attacked by boring through the largest whorl,
(the second) and generally in the same place, but were sometimes
eaten directly by Purpura pushing its proboscis past the oper-
culum or boring through it. When engaged in boring into these
relatively small Gastropods the Purpuras lie on their "backs"
and use the foot as a sucker attachment. A few shells of living
Purpura lapillus itself were also found with incomplete borings,
indicating that the voracious borer may at times be a cannibal.
In other localities Patella seems to be only rarely attacked,
and B. balanoides is the main prey. It is possible that the
prey may vary seasonally, but I know of no regular observations
on the subject.
In view of the diversity of the prey of Purpura, and its varia-
tion in different habitats, it would be of interest to know more
about the feeding habits of those stocks of Purpura which
are in constant contact with oysters, as they are in the River
Blackwater and off Whitstable.