OYSTER-DRILLS IN THE ESSEX ESTUARIES. 299
their rasping tongue, or radula, and eating the flesh of the oyster
through the hole so made.
Two oyster-drills are common on most English oyster beds,
namely, Ocinebra erinacea (=Murex erinaceus) and Purpura
lapillus; these are known in the Thames Estuary area as the
rough and smooth whelk-tingle respectively.
OCCURRENCE OF UROSALPINX IN ENGLAND.
Recently the American oyster-drill, Urosalpinx cinerea, a
form closely related to the British oyster-drills, has been found
in considerable numbers on the oyster beds in the River Black-
water, Essex (2), and there can be little doubt that this voracious
American oyster pest has been introduced into English waters in
shipments of American oysters in the same way as Crepidula.
Urosalpinx has no doubt been present in English waters for many
years, but it remained undetected until experiments were made
with Mersea oyster-drills in 1927 to find out the rate at which
these animals bore into and devour oysters (3). I have since
found individuals among material preserved in 1920, which is
therefore—at the moment—the earliest record we have of the
occurrence of Urosalpinx in England. It is not unlikely that
earlier occurrences may be recorded in the future if some naturalist
has collected and preserved individuals by chance at some time
prior to 1920.
So far Urosalpinx has only been recorded from the oyster
beds in the locality of the River Blackwater, but it will probably
be found to occur in other parts of the Thames Estuary and
possibly in other regions when its general appearance is more
widely known. This oyster-drill is, however, very similar at
first sight to Ocinebra erinacea, but the beautiful photograph
of these forms shown in Plate XXIV. (for which I am indebted to
the Essex Museum), will render the discrimination between these
two species a relatively simple matter. In the same photograph
are shown shells of Purpura lapillus, the so-called smooth tingle,
which occurs along with Ocinebra and Urosalpinx on the Black-
water oyster beds. In the autumn of 1928 samples of living
tingles dredged in the River Blackwater were forwarded to me
(by the courtesy of the Tollesbury and Mersea Native Oyster
Co.) and the following numbers and percentages (approximate)
(4) were found :—