36
THE ESSEX NATURALIST.
to reach the ground, in compensation for the lengthening of
the legs, and was an alternative arrangement to the lengthening
of the neck as familiarly seen in the giraffe. At this point in
the evolution of the group, the function of the prehensile trunk
evidently developed, and the later species of Tetrabelodon show
a rapid reduction in the rostrum, which would inevitably impede
the free action of the trunk. In Dinotherium, and in the true
elephants, one may observe how the chin is turned down, out
of the way of the trunk. These evolutionary changes are well
described in the Natural History Museum Guide to the Elephants.
The lower jaw of our Clacton baby elephant is illustrated in
Plate 6, in comparison with that of an older individual. The
antepenultimate milk molars (M.M. 2), of which the empty
alveoli are to be seen in our specimen, are the first real cheek-
teeth usually present in the elephants, the pre-antepenultimate
milk molars (M.M. 1), being vestigial.
The Mollusca.
These have been worked out by Mr. A. S. Kennard and Mr.
B. B. Woodward, with the care and accuracy which always
distinguish their investigation, and they have brought the list
of species up to 82, the longest from any English Pleistocene
deposit.
Shells are very abundant ; the most conspicuous to the casual
observer is Unio littoralis, which attains its maximum size at
Clacton. After a heavy sea I have often seen the beach strewn
over with these fossil shells, many of which are strong enough
to withstand a certain amount of rolling without disintegration.
They occur in the position of life, with the hinge-ligament still
preserved, but it is not easy to keep the ligament from cracking
to pieces on drying.
The well-known Pleistocene species, Corbicula fluminalis is
only known at Clacton as a derivative from the overlying
estuarine beds.
Mr. Kennard concludes that the place of the Clacton elephant
bed in the Taplow, or Middle, Terrace series of the Thames
basin is later than the Corbicula and Hippopotamus beds of Little
Thurrock (Grays), but earlier than the brickearths of Crayford
where the northern Elephas primigenius (unknown at Clacton)
is replacing E. antiquus.