THE DECAPOD CRUSTACEA. 183 



also hairy, and in life lies at the sides of the carapace, pre- 

 venting the access of mud to the posterior part of the gill- 

 chamber. These legs are also periodically unfolded, and 

 their terminal brush of hairs used to clean out the groove 

 and remove any adhering particles. This curious manoeuvre 

 may often be seen in forms kept in confinement. We have 

 already noticed the similar cleansing process practised on the 

 sensitive feelers. 



The special characteristics of P. platycheles are its general 

 hairiness, and the large size and flattened shape of the cheli- 

 peds. The front of the carapace is furnished with three 

 triangular teeth, the middle one being the largest. 



The minute porcelain - crab (P. longicornis) usually 

 measures in large specimens under a quarter of an inch 

 across the carapace. In the males the colour is bright red, 

 but is somewhat less brilliant in the females. The great 

 claws are of unequal size, and are more or less prismatic in 

 shape. Like the rest of the body, they are quite smooth 

 and devoid of hairs a marked contrast to the preceding 

 species. In the male, however, the " fingers " (chelae) of the 

 left great claw r are curiously twisted, and covered internally 

 with a dense pubescence of brown colour. The "fingers" of 

 the female are less markedly twisted, and the pubescence is 

 absent. In both sexes the antennae are about twice as long 

 as the carapace, and the front of the carapace is furnished 

 with three teeth, of which the middle one is deeply 

 grooved. 



Both the porcelain-crabs are abundant at most parts of the 

 shore, and live well in confinement. 



The next family is the PaguridaB, including our own very 

 curious hermit-crabs and the cocoanut-crabs of the tropics. 

 All these have long abdomens, like true Macrura, but the 

 abdomen is more or less soft, unsegmented, and usually un- 

 symmetrical. Most of the forms have in consequence 

 acquired the curious habit of availing themselves of the 

 shells of other animals, usually Gasteropods, and carrying 

 these about with them as a house. The appendages of the 

 abdomen are correspondingly reduced, the chelipeds are very 

 large and usually of unequal size, and the two last pairs of 

 walking legs are reduced. 



The true hermit- or soldier-crabs belong to the very large 



