THE CRUSTACEA 



133 



but occurs higher up in tide level. In fact, the two species 

 occur in exactly inverse proportions as regards tide range : 

 Palcemon squilla being very scarce low down, where its 

 larger relative becomes more abundant. 



Those who only know the prawns in the " cooked " con- 

 dition can form but a small idea of their beauty when 



Fig. 52. A. Palatmon serratus ; B. Pakvmon squilla. f Natural size 



living. They are of a translucent grey tint, striped trans- 

 versely with waved lines of deep olive-green and purple. 

 Their lovely tints and graceful movements make them 

 very desirable objects for the aquarium (see Fig. 52). 



Palcemon varians is a smaller species, closely allied to 

 the last, but only found where the water is of low density 

 estuaries of rivers and brackish water ditches where high 

 spring tides have access. It is abundant in the Thames. 



