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THE ESSEX NATURALIST
Order Filibranchia
Mytilidae
Modiolus barbatus (Linnaeus)
Moderately common; recorded from stations TL.2, TL.3,
Co, HB. 2 and from line 1, Stn. 4.
(The classification given above follows that used by Davis
in the original fauna list. Localities given for these new records
are those of the nearest labelled station on the map given by
Davis, 1967, fig. 2.)
Whilst examining some of the material dating from the sur-
veys of the Blackwater conducted by Davis, the present authors
had occasion to check some of the identifications appertaining
to the "type collection of many of the specimens" upon which
Davis's fauna list was based. As a result of these investigations,
four changes to the 1967 fauna list are required. These are:
Stylarioides monilifer Delia Chiaje (Davis, 1967, p. 23) must be
changed to Stylarioides plumosa (Muller);
Cheirocratus sundevalli (Rathke) (Davis, 1967, p. 31) must be
changed to Cheirocratus intermedius Sars;
Portunus marmoreus Leach (Davis, 1967, p. 34) must be changed
to Macropipus holsatus (Fabricius); and
Pinnotheres sp. ("The species may be P. pinnotheres") (Davis,
1967, p. 35) can be changed to Pinnotheres pisum
(Pennant).
Distribution of the Benthic Fauna
A total of 91 species of macroscopic benthic invertebrates
was obtained by the 1970 survey using the grab and dredge. The
great majority of these species were each recorded from only a
few of the stations sampled, in fact nearly 50% of the species
were each known from less than 4% of the stations within the
Blackwater. Less than 9% occurred in more than 40% of the
stations (Table 1). The 'average distribution' was such that a
species was found in 14% of the stations within the Blackwater
and in 13% of the total stations investigated. The frequency
of the 21 species which occurred in more than 20% of the Black-
water stations is shown in Table 2.