Decapod Crustacea of Bermuda, Part II. 63 



from its socket. These organs are particularly large and well 

 developed in A. candci and A. packardii, both of which make a 

 loud noise. (See figures of the chelae, pi. i<>, tigs. 30, 36', pi. 24, 



fig. 2.) 



This structure is lacking in Synalphcus, but present in Amphi- 

 bct(cn.\: Carpus of large chela is short, hemispherical, not cup- 

 shaped ; merus is short, triquetral. 



Second pair of legs slender; carpus with five unequal articles, 

 the first rarely longest. Other legs stouter, usually compressed, 

 generally with a simple dactyl; sometimes biunguiculate ; some- 

 times without a hook; propodus strongly spinose; fifth pair 

 smallest, with a brush of hairs and spines on the propodus. 



Second pleopod of the male has two retinules on the inner edge 

 of the inner lamella; the lower one has the distal part covered 

 with minute curved hooks, dilated at the tips (cine-mules'). These 

 also occur on the single retinules of the succeeding pleopods of 

 both sexes and serve to hold together the pleopods of the right 

 and left sides. 



Uropods large. Telson stout ; the end is wide, usually obtusely 

 rounded, without prominent angles, and bordered by numerous 

 long plumose hairs with spinules at the bases* (see pi. 27, fig. is) ; 

 dorsal surface has four spines. Anal tubercles well developed. 

 Five pleurobranchiae ; one arthrobranchia ; eight epipods ; some- 

 times an additional arthrobranchia. The larvae usually hatch in 

 the mysis-stage. Some of the species become 75 to 80 mm long. 

 Colors are often conspicuous ; they may be in stripes, bands, ocelli, 

 etc. 



All the species of this genus and Synalpheus are notable for the 

 loud snapping noise that they make.t 



This is a very remarkable habit, doubtless developed for defen- 

 sive purposes. When collecting these crustaceans by turning over 

 stones or breaking up dead corals one often hears an almost con- 

 tinuous fusillade, even when but few individuals are visible. Some 

 species make a much louder noise than others, independently of 

 their size. We find much difference in the relative size and form 



* These hairs and the similar ones of the uropods and antennal scales 

 are usually omitted in the figures. 



t A similar sound is made by the species of Gonodactylus, of the family 

 Squill'ida, often living in the same places, though the claw is entirely 

 different in structure. 



