8i 
ABUNDANCE OF THE SLIPPER LIMPET 
(CREPIDULA) IN ESSEX WATERS. 
(With Plate II.). 
ROBABLY one of tlie most remarkable instances of 
X the increase of an alien species in England is afforded 
by the American "Slipper Limpet" (Crepidnla forni 
cal a). This marine mollusc was first noticed in Essex by Mr. 
Walter Crouch, who on the 6th of September 1891 found a 
dead shell at Stone Point, St. Osyth, and exhibited it at a meeting 
of the Essex Field Club the next day (see Essex Naturalist, v., 
260). In a consignment of shells from the Crouch River sent 
to him on the 4th of March 1893, was a living example, the fish¬ 
erman (John Bacon) calling it a " Crow Oyster." Bacon said 
that he could remember them for 15 or 20 years, but they were 
very scarce. Subsequently Mr. Crouch communicated further 
notes (E.N., x., 253). He had received about 30 specimens 
from the Oyster Layings in the River Crouch. Dr. Laver 
presented to the Museum of,the Club a very large specimen 
attached to a stone, from the River Colne. Then observations 
followed in rapid succession in the journals, and years later 
Dr. Murie in the Zoologist (15th November iqii) summed up 
the occurrences in the Kent and Essex beds, and stated that in 
the Blackwater fisheries alone 35 tons of these shells had been 
dredged up within four weeks. 
Since then the increase has been most astonishing. We have 
no precise information from Kent, but in the Colne Estuary Mr. 
G. L. Trussed, the Manager to the Colne Fishery Board, informs 
us that during the past three or four years “ unabated efforts 
have been made to collect these limpets from areas most affected, 
and hundreds of tons have been taken by the dredge. In the 
course of the last twelve months upwards of 1,000 tons, taken 
chiefly from the estuaries of the Blackwater and the Colne, 
have been crushed and used for manure by the farmers of the 
districts." By the courtesy of the Editor of the Essex Standard 
we are enabled to print a picture [Plate II.), which gives a vivid 
idea of the immense quantities of the shell in the River Black¬ 
water, The crushing of the limpets is carried out in a large 
barge fitted with powerful machinery driven by an oil engine. 
In the picture some of the workmen are seen measuring out the 
crushed product into a lighter for delivery to a farmer. Our 
F 
