CRUSTACEANS 



Though Surrey has been for an indefinite period within easy reach 

 of competent naturalists, it has not tempted any of them to make a 

 systematic investigation of its carcinological fauna. The present chapter 

 derives benefit from the researches of Dr. Baird and a few others, rather 

 because they happened to carry them on in the neighbourhood of London 

 than because they had any special intention of exploring this county. 

 Nevertheless the area in question undoubtedly contains species of no little 

 interest in several divisions of the crustacean class. It will also appear 

 from some discoveries that many more may reasonably be expected to 

 follow. 



In certain parts of the world the higher groups of the Malacostraca 

 are well represented both on land and in fresh water. But this is not 

 the case in England. Of the Brachyura or * short-tails ' we have no 

 terrestrial or fluviatile species, no land crabs or river crabs. Here also 

 the fresh water yields but a scanty supply of Macrura or ' long-tails.' 

 Of these Surrey, like many other inland counties, can only claim with 

 confidence a single species, the common river crayfish, Potamobius pallipes 

 (Lereboullet). 1 In reference to this species two questions are not uncom- 

 monly mooted, one concerning the difference between a crayfish and a 

 crawfish, the other concerning the difference between these and a lobster. 

 All three were in uncritical ages included in a common genus Astacus, 

 whereas now they are all three generically distinct. Crayfish and craw- 

 fish however are essentially the same word, and like other vernacular 

 names have the misfortune to be sometimes used interchangeably. In 

 drawing any distinction therefore it is important first of all to nail the 

 name crayfish hard and fast on to the fluviatile species (Potamobius^ the 

 river-liver), reserving the other name for the marine animal sometimes 

 called a rock-lobster. This, the crawfish, will be found to stand out 

 boldly and clearly distinct by its far greater size, by its roughened 

 carapace, by its exceedingly long and stiff second antennas, and by its 

 want of well fashioned claws or nippers. The crayfish, on the other 

 hand, is very like a little lobster, but it will be found to differ from the 

 true lobster (Astacus gammarus) by having a larger ' scale ' to its second 

 antennae, and by having the segment which carries the last pair of trunk- 

 legs movable upon the preceding segment instead of being firmly fixed 

 to it. There are also small distinctions easy to observe in the frontal 

 process known as the rostrum and in the caudal extremity known as the 



1 For the information that this is found ' in the Wey about 100 yards above Harris's boathouse at 

 Weybridge' I am indebted to Henry F. Field, Esq., writing from 17 Argyll Road, Baling, March 14, 1901. 



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