THE POST-PLIOCENE NON-MARINE MOLLUSCA OF ESSEX. 101
the examples of Limnaea palustris is noteworthy as it is the very
short dumpy form only known elsewhere in England from the
Pleistocene beds of Crayford and Erith.
As to the age of these shells we have but little to guide us.
Since all the species are known from the Pleistocene and all
characteristic Holocene shells are absent, we are inclined to
consider them as belonging to the older series, and in all
probability of the same age as the Clacton examples.
GRAYS.
The first notice of the deposit at Grays was by Professor
Morris in 1836 (4), but although the occurrence of shells was
noted no names were given. Two years later, however, he
published (5) a list of sixteen species Mr. G. B. Sowerby
describing the high spired variety of Valvata piscinalis as a new
species under the name of V. antiqua. In 1856 S. V. Wood's
Monograph on the Crag Mollusca was published (11) and on the
authority of Mr. Pickering, he recorded forty-nine species as
occurring there. The next list was by Professor Boyd Dawkins
in 1867 (12) and contained only nineteen names, but two years
later Mr. A. Tylor listed fifty-two species (14) Mr. Pickering
again being the authority. In 1882 (22) S. V. Wood, jun.,
noted that although Unio tumidus was abundant, he had never
found U. littoralis ; but he added that his father possessed
specimens from this locality given him many years before by Sir
Charles Lyell. The last list was in 1890 (31), when, after a
critical examination of all the existing material and published
lists, Mr. P). B. Woodward recorded twenty species on the
authority of their various recorders and thirty from existing
examples. It has been considered advisable to make a few
alterations, though no fresh material has come to hand, all efforts
to trace Mr. Pickering's specimens having failed. When the
last list was given, no example of Planorbis carinatus was known
from any Pleistocene deposit of the Thames Valley. It had
been recorded by Professor Morris, A. Tylor, and Professor Boyd
Dawkins from Grays, but as there had been such confusion
between this species and P. marginatus it was deemed prudent to
omit it. Since then it has been found in abundance at Ilford
and at the Admiralty Section, so it is now included for Grays on
the authority of Professor Morris, the first recorder. Balea
perversa and Hyalinia fulva have been omitted, S. V. Wood being
of opinion that the record of the former given by himself was an