DISTRIBUTION OF THE CRAYFISH IN BRITISH ISLES 355
their extermination because they were overfished by the local
inhabitants who "feasted upon them" (Smith 1932a).
In the past attempts have been made to introduce and to
establish continental species of crayfishes in British rivers, but
there is no account on record indicating that any of these ventures
were successful. The small size of our native species and its
somewhat, continuous distribution throughout the country have
prevented its commercial exploitation on any large scale, as local
populations would be easily overfished. Populations of our native
species have fluctuated in numbers as was shown by Duffield
(1933). He suggested that in Oxfordshire, crawfish populations
had shown drastic declines in the past at intervals of about 13 or
14 years. He attributed this periodic decline to disease, inter-
acting with other factors, and suggested that the causes were the
microsporidian Thelohania contejeani and the bacterium Bacillus
pestis astaci. Many of the county records cited below are taken
from sources published in the latter half of the last and the. early
part of this century, and the species may therefore no longer
occur at some of the places mentioned. Records communicated to
us personally are indicated by P.C. and those from samples of this
species in the British Museum (Natural History) are denoted by
B.M. The authors will be pleased to receive records or specimens
from localities not cited here.
England and Wales
BEDFORDSHIRE—R. Lea (Stebbing 1920). BERKSHIRE—R. Ock,
R. Kennet (Stebbing 1920a), Ham Bridge (B.M.), nr. Newbury
(B.M.). BUCKINGHAMSHIRE — Hovenden nr. Princes Ris-
borough (Stebbing 1920b). CAMBRIDGESHIRE—Bottisham Lode
(Lownes 1938). Wicken Fen (Gurney 1926). CHESHIRE—nr.
Altrincham, Tabley, R. Weaver trib., Withington nr. Chelford
(Tattersall 1920). DERBYSHIRE—Cringleford Bridge (Stebbing
1905), Bakewell to Haddon R. Wye (Lowe 1921). DORSET—Dor-
chester to Maiden Newton (Stebbing). ESSEX—R. Lea, R. Chel-
mer (Stebbing 1903), Twyford Mill, R. Rib (P.C). HAMPSHIRE—
Leckford (Haines 1945), W. Basngstoke (B.M.), R. Meon (B.M.),
Winchester (B.M.). HEREFORDSHIRE—Great Barwick Ford, R.
Arrow, R. Frome, G. Gamer, R. Garran, R. Leadon, R. Lugg, R.
Munnow, R. Teme, R. Wye (Stebbing 1908a), Dowles Brook (Anon
1898). HERTFORDSHIRE—R. Rib nr. Latchford (Pullen 1883), R.
Gade, R. Lea (Stebbing 1920c), Hatfield (B.M.). KENT—R. Darent
at Shoreham, Tunbridge Wells (Stebbing 1908), Eynsford (B.M.),
Dunton Green (B.M.). LANCASHIRE—Crime Lake nr. Bardsley
Canal, Droylsden nr. Manchester, Knott Hill reservoir Ashton-
under-Lyne (Tattersall 1920), Staveley-in-Cartmel (B.M..). LEICES-
TERSHIRE—no spec. loc. (B.M.). MONMOUTH—Cwmbran (B.M.)
NORFOLK—Aylsham R. Bure, Cringleford and Keswick R. Yare,
Ryburg Mill R. Wensum, Scarrow Beck Blickling, Taverham
Mill, Thornage R. Glaven, Thurning (Gurney 1926). NORTHAMP-