( -i ) 



The chelipeds are generally much stouter than the and and 3rd pairs 

 of legs : sometimes they are quite equal and symmetrical, but much oftener 

 one is very much larger than the other. The wrist and hand may lie in the 

 same plane with the merus, in which case the fingers move more or less 

 vertically ; cr they may be twisted so that their true outer surface looks 

 upwards, and then the fingers move more or less horizontally. The finger- 

 tips may be calcareous, or may be more or less edged with chitin. The 

 proportions of the chelipeds, the set of the hands, and the condition of the 

 finger-tips furnish characters that are important in classification. Occasion- 

 ally the hands, or one of them, are modified to form a door (operculum) to 

 the mouth of the shell or tube in which the animal lives. 



The 2nd and 3rd legs (only m the Lithodidce the 4th pair also) are the 

 organs of locomotion, and are consequently long and stout. Each, like the 

 chelipeds, consists of 6 joints, the basis and ischium being fused. They 

 may either equal or may considerably exceed the chelipeds in length, and 

 they may be symmetrical, or those of one side (usually the right) may be a 

 little the longer. Very often the propodite and dactylus of the third left 

 leg— these being parts that can be made use of by the animal to close its 

 shell ; or, in other words, parts that are of signal importance to the animal 

 in adapting itself to the environment— furnish characters of obvious specific 

 value in classification. 



The 4th and 5th legs are, in all typical Pagurines, very much reduced in 

 size, are useless for locomotion, and are used as grapnels to hold the shell, or 

 other adventitious tenement, fast. To this end the 5th pair are almost always 

 chelate, and the 4th pair subchelate (occasionally even chelate), and in both 

 pairs the distal end uf the propodite (and often of the dactylus also) has 

 on Its outer surface a well-defined patch of imbricating corneous granules 

 that recalls in some sort the sole of a house lizard's foot. Only in Birgus 

 and the Lithodidce do the 4th and 5th legs depart from this typical form. 

 In these the 5th legs are little better than rudiments, which are carried 

 inside the gill-chamber ; while as to the 4th pair, in Birgus they end in 

 rasp-like chelae of considerable size, and in the Lithodidce they are ambu- 

 latory legs like the two pairs in front of them. 



Occasionally in the male the coxaj of the 5th pair of legs (or one of 

 them) are produced, either in themselves or as to the vas deferens that per- 

 forates them, to form an intromittent tube often of almost fantastic shape. 

 Characters of classificatory value are thus afforded by the coxae of the 5th 

 pair of legs. 



The appendages of the abdomen vary greatly, and very rarely can be 

 of any use in locomotion. Except in the Lithodidce the caudal swimmerets 

 (" uropods ") are invariably present, and are commonly used as grapnels, being 



