20
THE ESSEX NATURALIST
The full list of specimens, obtained mainly by splitting the
small quantity of peat preserved in the Survey Museum, follows
below:
Feronia sp. Basal two-thirds of left elytron. It matches either
of the British species, nigrita ov anthracina.
Agabus cf. congener Pk. Metasternum, third coxae, post-coxal
process and 2nd sternite, joined.
Colymbetes fuscus L. Coxae, piece of metasternum and post-
coxal process, half sternites 2 and 3.
Rantus grapii Gyll. Metasternum, right coxa and post-coxal
process.
Hydrobius fuscipes (L.). A single complete elytron.
Helophorus aquaticus L. Head and pronotum joined, head.
Cercyon cf. minutus Muls. Left elytron and an associated pair
of elytra.
Thanatophilus dispar Hbst. Apex of elytron, half pronotum.
This has been distinguished from sinuatus because it has
a narrow but sharply defined explanate border to the
elytron, whereas in sinuatus the border is much wider and
less sharply demarcated.
Staphylinus cf. erythopterus L. Half pronotum.
Platystethus arenarius Geoff. Pronotum.
Aleocharine pronotum.
Aphodius spp. Five heads, an elytron and various other parts,
probably of at least three species.
Plateumaris cf. braccata Scop. Apex of left elytron.
Donacia semicuprea Pz. One complete underside, two pronota,
four right elytra, three left elytra, fragments of five other
elytra, three mesosterna, three metasterna, three femora,
three tibiae, one abdominal sternite.
Otiorrhynchus clavipes Bonsd. A head (broken); apex of two
fused elytra; also associated together, a large part of an
elytron, mesonotum and mesosternum.
Along with these beetles occur Diptera pupae and moss mites
(Acarina).
This assemblage gives a clear ecological picture. Donacia
semicuprea, the predominant species, feeds on Carex. The pre-
sence of a complete, though crushed, insect and many other parts
in association probably arises from the insect's habit of forming
a subaqueous pupal cocoon in which the imago emerges but re-
mains for some months submerged, sometimes never to escape.