CRUSTACEANS 



For the special fauna with which the present chapter is concerned 

 this county might very well be chosen as a representative region. To 

 such a preference the contributory circumstances are these : it occupies 

 a fairly central position ; it is richly diversified with hills and dales, 

 rivers and forests ; it is also abundantly supplied with wells, ponds, 

 gardens, and greenhouses. Under these favouring conditions a student 

 might probably make himself acquainted with the land and freshwater 

 crustaceans of England at least as well in Nottinghamshire as in any 

 equal area of the interior. It is not a question of competition with 

 maritime counties, where tidal rivers, harbours, brackish pools, and a 

 saline atmosphere may confuse the results. Only the truly terrestrial and 

 freshwater species are here to be taken into account. But while the 

 territory is very attractive for this limited branch of research, it must be 

 confessed that it is at present to a large extent virgin ground. Hitherto 

 only two or three investigators have published records of their researches. 

 Among these, as will be seen, especial acknowledgement is due to 

 Professor J. W. Carr, M.A., F.L.S., F.G.S., of University College, 

 Nottingham. 



Our inland fauna nowhere illustrates the whole class of Crustacea : 

 it is entirely barren of the highest and the lowest groups ; there are no 

 crabs and no barnacles. On the other hand, species intermediate between 

 these two extremes are far more numerous and far more common than is 

 generally suspected. An overwhelming proportion of these belong to 

 the Entomostraca, while comparatively few are distributed among three 

 orders of the Malacostraca. There is, in fact, only one out of the whole 

 number that answers to the ordinary popular notion of a crustacean. 

 This is the river crayfish, Potamobius pallipes (Lereboullet). The generic 

 name appropriately points to its life in rivers. Its extensive distribution 

 over the river-system of England is only now being gradually proved, and 

 is almost certainly subject to some limitations and fluctuations. The 

 latter are apparently due to epidemical disease or other temporary and 

 local disasters. The former may be traced to uncongenial conditions of 

 soil or climate, and will be worthy of more exact consideration when we 

 are more sure of the precise facts. That a particular district is fertile in 

 crayfish is easily proved by our finding plenty of specimens in it ; but by 

 not finding them we cannot at once conclude that there are none to be 

 found. We have to bear in mind the old logical warning that it is 

 extremely difficult to prove a negative. However, with regard to the 

 species now in question, the Rev. Joseph Walker, of Averham Rectory, 



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