44 
HISTORY OR BRITISH CRUSTACEA. 
the sandy beach between Hayle and St. Ives quite strewn 
with their exuviae, and he was informed by Mr. E. Couch 
that the Polybius is gregarious, swimming in shoals, and 
thus occasionally occurring in great numbers on the south 
coast of Cornwall. 
Polybius Henslowii. Henslow’s Swimming Crab . (Plate 
III. fig. 2.) — Carapace quite smooth and flat above. Body 
very depressed ; front with five triangular teeth. 
Pirst obtained by Professor Henslow on the north coast 
of Devon, and subsequently found in various parts of the 
southern coast of England. It was named by Dr. Leach 
after the learned naturalist who first discovered it. 
This is named Nipper Crab by the Cornish fishermen. 
Mr. J. Couch, in his ' Cornish Pauna/^ observes that this is 
more a swimming crab than any of the others ; “ for whilst 
the other British species of this family are only able to shoot 
themselves along from one low promontory to another, the 
Nipper Crab mounts to the surface over the deepest w r ater 
in pursuit of its prey, among which are numbered the most 
active fishes, as the mackerel and Eauning pollack ( Merlan - 
gus carbonarius ) , the skin of which it pierces with its sharp 
pincers, keeping its hold until the terrified victim becomes 
exhausted. We are witnesses of this curious method of 
* Part I. p. 71. 
