354 OCCURRENCE OF CREPIDULA FORNICATA, L.
taken about thirty specimens, mainly from the oyster layings in
the River Crouch; some being adherent to oyster shells and others
to stones, and in 1896 I discovered two full-sized specimens on
oyster-shells dredged from the River Colne, between Brightlingsea
and the Pyefleet. It is interesting to find that yet another has
occurred in this river. Dr. Laver's specimen is certainly the
largest which has yet been taken (measuring about 51 by
40 mm.), while the presence of a mass of yellow spawn yields
further proof that the mollusc is quite acclimatised and that
it now breeds in our waters.1
In my former notes is recorded the presence of eggs in a
specimen taken on April 15th on a stone, which is still in my
possession, and since then I have had several of these molluscs in
a "baby" condition, the youngest measuring 8 mm., which
were presented with a selection of four other shells to the
British Museum of Natural History.
Of the two Colne specimens of Crepidula, one is the largest
ever taken by me, measuring 43 by 33 mm., while the other
is 37 by 27 mm. Like the "monster" of Dr. Laver, the former
has but a tinge of fawn-brown colour, while the latter is of a
darker brown inside, with a series of marginal spots, and has
the epidermis on the exterior, through which the rayed mottlings
can be perceived.
In the general structure of the animal (which is attached to
the shell by the septum) and in the enamelled concave surface, there
appears little variation; but the shells exhibit very considerable
differences in size, in proportion of width to length, in coloura-
tion, and in convexity; these conditions being determined by
the shape and surface of the stone or shell to which they adhere,
and on which the 'scar' or pallial line may always be traced,
the enclosed surface of their attachment being quite smooth.
The epidermis or outer membrane of the shell is often partly
or wholly wanting, being either worn away, except on the outer
edges, or as sometimes happens through another of the same
mollusc being perched upon the top, and in some cases very
nearly as large.
It would appear that the animal leads a very sedentary
existence, and probably never removes (unless compelled) from
its first attachment. I have, however, one shell which has
1 At the Meeting on September 9th, 1897, Mr. W. M. Webb exhibited a specimen
attached to a foreign oyster laid down at Brightlingsea (see E.N., ante page 227).—Ed.