254 BUlvLETIN OF THE BUREAU OF FISHERIES. 



tends also to increase with age and in favor of the '"crusher," which in old males reaches 

 an extraordinary size (fig. i). Many crayfish when incautiously handled readily draw 

 blood, and there can be little doubt that a lobster weighing upward of 30 pounds could 

 easily crush a man's arm at the wrist. 



The differentiation of the large claws is often very marked in crabs, and all degrees 

 are represented. The character of the adaptation is equally varied, as may be seen in 

 the common green crab {Carcinus mcBnas), the fiddler {Gelasimus pugilator), and in the 

 "king crab" of the West Indies (Caleppa marmorata) . In Carcinus the slightly larger 

 claw is of the "knobbed" or crushing type. A singular differentiation has apparently 

 been started in the same direction in the more remarkable Caleppa, where the great 

 chelipeds have been modified in a different manner for the protection of the animal. The 

 great trihedral claws of this singular species swing in and out in front of the head like 

 double doors, and when these are closed or folded in, the crab is as secure as the tortoise 

 in its shell. 



In many of the small shrimps belonging to the Alpheus family, the huge "hammer" 

 claw, which is usually largest in the males, is most interesting, whether considered 

 as a "snapper" or popgun, as a saber for deUvering a slashing blow, or as a means of 

 controlling the development of its fellow in regeneration (see p. 277). 



But of all the crustaceans known to me the shrimp-like Jousseaumea which I found 

 at Nassau, Bahama Islands, in 1887, but did not describe, presents the most singular 

 differentiation of the claws. When viewed from above this animal presents a very 

 deceitful appearance, no formidable weapons of any kind being visible. In reaUty, it pos- 

 sesses a huge and ugly looking claw, which in rest is completely concealed, being nicely 

 folded Uke a pocket rule and tucked under the grooved cephalothorax, ready at any 

 moment to be shot out and to strike an unsuspecting victim. The fellow to this 

 "pocket" weapon is very diminutive. Were this little shrimp as large as the common 

 lobster it would be justly regarded as one of the most remarkable animals in the sea. 



While in Cambarus and in crayfishes generally right and left claws may be more 

 or less unequal in size, they are often very similar in structure and function, suggesting 

 the primitive toothed type seen in the lobster, but not approaching it with any degree 

 of detail. There is no lock spine in Cambarus, but the hooked tips cross, the dactyl 

 underlapping the propodus. The armature consists of small rounded tubercules, set 

 like a row of com on a cob. When this claw is closed a large gap is left at the proximal 

 end where the teeth are most numerous, and the fingers touch only at their tips. 



THE GREAT CHELIPEDS. 



The legs which carry the big claws consist of the 7 typical segments already enu- 

 merated (pi. xxxvii), united to the body and to each other by articular membranes, 

 and moving in the way described on double hinges of variable form, excepting only 

 the basis and ischium, or second and third segments, which after the fourth or fifth 

 stage fuse into a single piece. This limb in the adult state therefore possesses 6 free 

 podomeres and 6 free joints. The suture of the stiff joint {x in all figures) marks the 

 "breaking plane," since whenever the lobster "shoots a claw," the limb always breaks 

 at the suture of this joint. 



