300
BRITISH OYSTERS : PAST AND PRESENT.
Supplementary Notes.
By ALFRED BELL.
THE following notes mainly refer to the local distribution
of the various groups, or isolated forms, present in the
recent British Seas, or in the later Pleistocene and Holocene
deposits.
In many localities, especially in the S. and S.E. of England
and parts of Scotland given over to Ostraeculture, the original
mollusc has been wholly or partially replaced by the introduction
of Exotic types, but the earlier inhabitants can usually be de-
termined by an examination of the dead shells often seen in situ
between tide marks. To the Roman settlers in Britain is due
the introduction of these culture nurseries in Kent (ante, p.
207), where they imported and raised their home favourites
(Figs. 11, 13). I have found these introduced forms amongst
Roman debris received from Folkestone, sent me by Mr. H.
Warren, and from Verulam, given me by Mr. Bullen, of the
Saint Albans Museum.
West Scotland is a veritable museum of ancient types and
new arrivals. The Loch Sween O. stentina probably came with
a large consignment of Arcachon shells which was relaid here,
as I am informed by Mr. Calderwood, of the Scottish Fishery
Board, to whom I am indebted for much information and the
gift of specimens. 
The shell is apparently one of the many modifications of a
variable group, of which Monterosato enumerates a dozen. It
does not quite agree with specimens of Arcachon oysters sent
me by Mr. Robert Dollfus of the French Bureau Scientifique
des peches maritimis, either in sculpture, the ribs being much
closer and acute, or in colour. This may be due to environment,
owing to the conditions under which the oysters are reared. Mr.
Calderwood also found a small colony of quite recent date at
Arisaig of a private inlaying from Colchester.
Some typical Carse Clay Oysters are of the old pointed
"Pandoure" type but are smaller and stronger in the ribbing
and evidently lived to a great age, if I may judge from specimens
kindly lent me by the Geological Survey Museum, Edinburgh ;