SOME OBSERVATIONS ON THE CLADOCERAN 363
Arion ater (L.). The Black Slug, found on a few occasions in
damp places such as around ponds and on the sea wall. It
is probably common.
Family Zonitidae
Oxychillus cellarius (Muller). Common in all damp places, but
particularly along the edges of the drained marsh and also
among brick rubble.
Family Vitrinidae
Vitrina pellucida (Muller). Shells found on the side of a dry ditch
at West Mersea and in some hedgerows.
Family Limacidae
Limax maximus L. The variety vinosa of this species was found
on two occasions on the bed of a dried-up pond near the
Fountain Hotel, West Mersea. Probably common.
Agriolimax agrestis (L.). Common in damp places, in meadows,
ditches and beside ponds.
References
Ellis, A. E. (1926). British Snails. Oxford University Press.
Ellis, A. E. (1951). Ed. Census of the distribution of British non-marine
Mollusca. J. Conch., 23: 171-244.
Macan, T. T. (1960). A key to the British fresh and brackish water
gastropods. Freshwater Biological Association Scientific Paper
No. 13.
Some Observations on the Cladoceran
Scapholeberis mucronata (O. F. Muller)
By C. S. Reynolds
The presence of a natural population of Scapholeberis
mucronata (O. F. Muller, 1785) in an ornamental garden pond
provided an excellent opportunity for the study of this extremely
interesting Cladoceran. Observations extended from April 1964
to July 1965, and form the basis of the following account. Addi-
tional information has been derived from the literature.
According to Scourfield and Harding (1958), S. mucronata
(O. F. Muller) occurs in ditches and ponds, and in sheltered bays
of larger lakes. Such locations are characterized by a calm surface,
which appears to be an essential prerequisite for colonisation by
Scapholeberis.
The pond to which the present observations refer is in a garden
at Upminster, Essex. It is approximately rectangular, 3.5 metres
x 1.2 metres, and with a maximum depth of slightly more than
0.5 metres. The basin is of concrete, with vertical sides, and the
edges are horizontal. Changes in water level were due almost