62 Addison E. Verrill, 



Development is various ; most species have small eggs and a 

 zoea stage at first ; others hatch in the my sis stage ; some have 

 few large eggs and hatch in a very advanced condition. Most of 

 the species, if not all, retain the larval median ocellus through life. 



The species are numerous in all tropical and semitropical seas. 

 Most of them live in holes in rocks, dead corals, sponges, etc. or 

 under stones ; some make burrows for themselves in mud or sand ; 

 few live more or less free and exposed. Nearly all live in shallow 

 water. Many have protective colors. All are predacious and 

 usually pugnacious, often killing one another, in aquaria, by means 

 of the large chela. 



In moulting the large chela, carpus, and some of the other 

 articles split in moulting to facilitate the operation. 



Alpheus Fabr. or Crangon Weber. Snapping Shrimps. 



Alpheus Fabricius, Supl. Ent. Syst., p. 38, 1798. H. M.-Edw., op. cit, 

 1837. Dana, op. cit., 1852. Coutiere, op. cit, p. 336, 1899. 



Dienesia Woodward, Ann. and Mag. N. Hist., 1835, p. 552. 



Crangon Weber, p. 94, 1795 (pirated name). M. J. Rathbun, op. cit., 

 1904 p. 170. 



This is a very extensive genus very diversified in structure and 

 forms. The eyes are usually completely covered by a thin lobe of the 

 carapace, separated from the rostrum by a sinus or groove. Ros- 

 trum plain, small, usually acute, spiniform or triquetral, and 

 longer than the ocular lobes ; sometimes nearly or quite abortive. 



Chelae of the first pair of legs are very unequal ; one is very 

 large in both sexes, usually notched, often deeply grooved, some- 

 times plain. It has the dactyl short, variously arched, stout, and 

 often blunt, furnished on the inner surface, near the base, with a 

 prominent lobe or plunger that fits into a pit or socket of the 

 thumb when closed. This is used in producing a sharp click or 

 explosive sound when disturbed. (See pi. 22, figs. 3, 6a; pi. 24, 

 figs. 3-6; pi. 21, fig. 3.) It is present also in Synalpheus and 

 Amphibet&us. 



On the posterior end of the dactyl, above the hinge, there is in 

 most, if not all the species of this genus, a small, firm, more or 

 less circular ring, enclosing a flexible disk. This perfectly matches 

 a similar organ on the anterior articular surface of the palm. 

 They seem to serve as suckers to receive and hold back the dactyl 

 at the opening of the claw when the plunger is suddenly withdrawn 



