250
THE ESSEX NATURALIST
Diadumene cincta Stephenson* is present in small groups or
as isolated individuals and is also a member of the commensal
association with Polymastia. Many sagartiids are present.
Sagartiogeton undata (Muller) (=Actinothoe anguicoma (Price))
is attached to stones, embedded in holes in the bricks or in tubes
in the mud adjacent to the dam. It, also, is a member of the
commensal group. Sagartia troglodytes (Price) is also plentiful.
Flatworms have not been found but there is a very large
nematode population present in the mud and in the growths of
encrusting sponges; and what appears to be a nemertine re-
sembling a small Amphipoms but with a curiously thick and
transparent epidermis.
Two placophora, a Callochiton and an Acanthochitona, have
been found, but surprisingly few gastropods are present on the
dam. Some small specimens of Gibbula cineraria (L.) are all
that have been found, although many Littorina and Crepidula
larvae are present in the plankton. Scattered groups of Mytilus
edulis L. are present often covered by the dominant barnacle
Elminius modestus Darwin, and small specimens of Venerupis
pullastra (Montagu) (up to 25 mm.) occur in muddy sand between
the stones. Large shells of Pholas dactylus L. have been found,
but no living specimens. The last may, however, be present in
the firm mud on the far side of the island and all the "piddocks"
appear to be present on the Naze. Single specimens of Cardium
edule L. and Modiolus modiolus (L.) have also been found.
In view of the extensive barnacle population it is surprising
that the dog whelk (Nucellus lapillus (L.)) is absent. Is this due
to a dislike of the calm water or to the fact that Elminius is an
unsatisfactory food?
Polychaete Worms
Nereis diversicolar O. F. Muller and Nephthys caeca
(O. F. Muller) are present in fair numbers, although small.
A "red threads" (Audouinia sp.) has also been found and
two specimens of Amphitrite johnstoni Malmgren. One of
the latter was a well-grown specimen and contained in its
tube a large specimen of the scale worm Harmothoe lunulata
(Delle Chiaje). The terrebellid was particularly interesting be-
cause it inhabited a burrow in the mud-filled crack of a pile
immediately beside an apparently similar tube containing a red
*The species presented difficulties for a time and was thought to be a
young stage of Metridium. Examination of living specimens,
however, at all stages from contraction to complete expansion,
and comparison with the description given hy Stephenson (1935),
left no doubt as to their identity. The anemones fitted the de-
scription in a most complete and satisfying way.
It is of interest to the Club that Professor Stephenson in-
cludes a note by Dr. N. H. Howes reporting the finding of
Diadumene cincta in New England Creek, in February, 1933,