THE LAST INTERGLACIAL NON-MARINE MOLLUSCA 13
and M. primigenius as being the equivalent of Zones IIb and
III of the Ipswichian. Trafalgar Square has also been shown to
be Zone f (Zone II) by Franks (1960). Ipswich is the type
locality for the Ipswichian, so from the standpoint of the flora,
the Aveley, Trafalgar Square, Ilford and Ipswich sites are of
comparable age.
The Aveley aquatic molluscs are indicative of hard water
(defined from the standpoint of molluscs as not less than 20
mg of calcium per litre (Boycott 1936, 149)), as may be expected
from a river flowing through Chalk areas in its upper reaches.
The fauna is indicative of slow-moving water with marshy or
swampy areas. The presence of limacid slugs' "shields", though
quite robust enough to withstand long aquatic transport, sug-
gest that woodland was not too far away. Bythinella scholtzi
stands out by its abundance at Aveley; in contrast, it is not
known from Ilford, Ipswich or Trafalgar Square. It has a some-
what sporadic occurrence in the British Pleistocene, being
known from the Cromerian (Lower Pleistocene, West Runton,
Norfolk), the Upper Pleistocene and Holocene. It is recorded
from the Last Interglacial at Histon Road, Cambridge, Zones
h-i (now Zone IV), by Sparks (1964). It died out during the
Holocene but was re-introduced to Britain in 1900 from
America. It now lives in canals in Cheshire and Lancashire and
a dock at Grangemouth, Stirlingshire. The systematic position
and identity of Paladilhia radigueli is uncertain (Sparks 1964,
14-15). It may be a freshwater species akin to Lartetia, and
not as usually regarded, a brackish-water hydrobiid. Its pre-
sence at Aveley should not be taken as indicating some degree
of salinity. Belgrandia marginata is entirely typical of the Last
Interglacial, a southern species now living in clean spring water
in a few localities in the Pyrenees and southern Alps, but also
surviving to the end of the Interglacial in England as a rarity
(Sparks 1964, 15). The bivalve Corbicula fluminalis, although
represented in the samples by only one hinge fragment from
Sample F, was reported by the excavators of the elephants to
be quite common in the middle and lower beds at Aveley, but
none appear to have been collected. It lives today in North
Africa and Asia. It was found at Ilford but not at Trafalgar
Square or Ipswich. The molluscs of Aveley then are those pre-
ferring warm to temperate climates. No forms indicating a
cold climate were collected.
Although the mollusc faunas are broadly similar at Aveley,
Trafalgar Square, Ilford and Ipswich, each has its peculiar ele-
ments. For instance, the mussel Margaritifera auricularia
(Spengler) has so far been found only at Trafalgar Square.
Similar sporadic occurrences at these sites should not be given
any deep meaning. In the author's field experience, habitat
conditions can vary widely within a small area, and even within
one pit only part of the general fauna of the area may be col-