350
THE ESSEX NATURALIST
the British Isles. Later, Dr Isabella Gordon confirmed that our
specimens were A. pallipes by comparing them with Lereboullet's
types of this species in the Paris Museum (Gordon 1963). In June
1964, through the courtesy of Dr Richard Bott, we were able to
examine specimens determined by him as Austropotamobius
(Atlantoastacus) pallipes pallipes and included in his 1950 paper.
One of these, a female of 85 mm total length from Frieburg in
Breisgau, Baden, Germany — has an abnormal rostrum because
it lacks apical rostral spines. It is possible that this specimen
was the one chosen by Bott when he compiled the key
characters and diagnosis of this species, for he is quite affirma-
tive about the absence of these rostral spines in his concept of
the species.
The spines are clearly present in Lereboullet's types of A.
pallipes and in all specimens examined by us. Bott recognised
three subspecies of this crayfish, A. (A). pallipes pallipes (Lere-
boullet 1858), A. (A). pallipes italicus (Faxon 1914) and A. (A).
pallipes lusitanicus (Mateus 1934). Although our specimens
from the River Darent are clearly different from the subspecies
lusitanicus they show a combination of the characters listed by
Bott for distinguishing the subspecies italicus from pallipes. For
similar reasons Karaman (1962) rejected Bott's subgenus Atlan-
toastacus. Because of this difference of opinion we suggest that
our native species should be designated, for the present, as
Austropotamobius pallipes (Lereboullet). The illustrated key by
Hynes et al 1960 is adequate for distinguishing A. pallipes from
other European species that may have been introduced into British
rivers.
The bionomics of Austropotamobius pallipes in a section of the
River Darent.
The following observations are based on collections made in a
section of the River Darent, Kent between early October 1963
and October 1964.
Methods
The part of the river selected for this study is sited opposite
the Kent River Board pumping station at Eynsford. We choose
a 400X4 m section of the river in which the water depth varied
between about 150 and 600 mm. The river bottom graded from
coarse shingle to fine mud and was strewn with stones and rocks.
From June until October the shallowest parts were carpeted with
dense growth of Elodea canadensis.
The river flooded twice during our study, once in October
1963 and again in March 1964. On each occasion the topography
of the river bed was changed. Because of these variable con-
ditions we found only one satisfactory method for collecting cray-
fishes in our section. A small handnet was held with the lower
edge of its frame against the river bed and with the net opening