104 THE POST-PLIOCENE NON-MARINE MOLLUSCA OF ESSEX.
We have also been able to verify from the same source four
records of which no examples were known :—
Limnaea stagnalis Anodonta cygnaea
Planorbis carinatus Sphaerium corneum.
Of the new records, two are of great interest :—Helicella
virgata and Pupa cylindracea. The former is known from the
Pleistocene of Barnwell, near Cambridge, but has hitherto been
unrecorded from the Thames Valley in either the Pleistocene
or Holocene. This is the more remarkable as it is an abundant
form at the present time. Pupa cylindracea has only once been
recorded from the Pleistocene—namely, from Clacton—and even
in this case the record is extremely doubtful. It is unrecorded
in the Thames Valley from the beds of either age, though it is
common at Copford.
The addition of Pisidium astartoides was to be expected, since
until lately it was only considered a variety of P. amnicum. In
the Museum of Practical Geology are two shells of exceptional
size from Ilford—an example of Limnea palustris measuring
29 mm. alt. and one of Bythinia tentaculata 15 mm. high. A
Limnaea in Dr. Corner's collection differed so much from all
British forms that we submitted it to Dr. O. Boettger, of Frank-
fort, and we would here take the opportunity of expressing our
thanks for the trouble he has taken in the matter. He remarks
that it is quite new to him, but is near to L. palustris var. diluviana,
And. As we are of opinion that it is undesirable to describe new-
species or varieties from single examples, we have considered it
a variety of L. palustris for the present, with the hope that more
examples may be found, so that its true position may be
ascertained.
In 1869, during the discussion following Professor W. B.
Dawkins' paper "On the Distribution of the British Post-glacial
Mammals" (Q.J.G.S., vol. xxv., p. 192), Dr. Gwyn Jeffries
mentioned that Pyramidula ruderata and Elliotti fruticum occurred
at Ilford. The latter record is, of course, correct, but our efforts
to trace any examples of the former have been unsuccessful.
Dr. Jeffries' collection is in America, and in answer to our
enquiry Mr. W. H. Dall wrote that there were no examples of
P. ruderata from Ilford ; but as there is no inherent improbability
in the record, we have listed it on the authority of Dr. Jeffries.