306
THE ESSEX NATURALIST.
there is little difference in size, though possibly those of Ocinebra
may be found to range to the largest size.
There is little doubt that the harmful character of the oyster-
drills is not fully realised on English oysters beds and that drastic
action, where this is economically possible, should be taken to
keep down these pests to reasonable numbers, if oyster culture
is to be carried on with success. Observations on the habits and
distribution of these pests may therefore be of economic value
as well as of scientific interest.
SUMMARY.
Three oyster-drills or borers occur in the River Blackwater,
Essex, namely Ocinebra erinacea, Purpura lapillus and Urosalpinx
cinerea. The latter is the American oyster-drill and has with
little doubt been introduced on American oysters. The date of
the introduction of this pest is unknown, but occurred at some
time before 1920. Urosalpinx and Ocinebra bore into and eat
small (brood) oysters in about three days and larger (half-ware)
oysters in 5 to 6 days.
The shell and egg-capsule characters of the three forms are
shown and their habits are discussed. It is shown that the
feeding habits of Ocinebra and Purpura vary in different habitats.
The importance of the suppression of these pests for successful
oyster-culture is emphasised, as well as the economic importance
of a knowledge of their habits.
REFERENCES.
1. Is the American slipper-limpet (Crepidula fornicata) an oyster pest ?
J. H. Orton. Nature, vol. 117, 1926, p. 304.
2. The occurrence of the American oyster pest, Urosalpinx cinerea (Say)
on English oyster beds. J. H. Orton and R. Winckworth. Nature,
vol. 122, 1928, p. 241.
3. The habits and economic importance of the rough whelk-tingle
(Murex erinaceus). Nature, vol. 120, 1927, p. 653.
4. Report of the Council. Journ. Mar. Biol. Assoc, vol. xvi., No. I,
1929, p. 348.
5. Federighi (in litt, not yet published).
6. Habitats and feeding habits of Ocinebra erinacea. J H. Orton.
Nature, vol. 124, 1929, p. 370.
7. Rheotropism in Urosalpinx cinerea (Say). H. Federighi. Biol.
Bull, vol. lvi., 1929, p. 331.
8. British Conchology. J. G. Jeffreys. Vol. 4, p. 308.
9. The oyster-drills on English oyster beds. J. H. Orton and C.
Amirthalingam. Nature, vol. 124, 1929, p. 298.