2IO REPORT OF NEW JERSEY STATE MUSEUM. 

 Key to the Genera. 



a. First gnathopods subchelate in both sexes ; size moderate. orchestia 



aa. First gnathopods simple in female ; size large. talitrus 



Genus ORCHESTIA Leach. 



Orchestia Leach, Edinburgh Encyclop., XI, 1813, p. 326. Type Cancer Gam- 

 marus littorcus Montagu, monotypic.^ (Not consulted.) 



? Psammylla Rafinesque, Amer. Month. Mag. Crit. Rev., II, November, 1817, 

 p. 41. Type Psammylla littoralis Rafinesque, monotypic. 



? Psammopsylla Rafinesque, nom. orig. 



Orchestes, auct. 



Body more slender and compressed than in Talitrus. First 

 pair of coxal plates rather small, fifth pair almost as deep as 

 preceding and deeply bilobed. Cephalon, antennae and oral parts 

 almost exactly as in Talitrus. Anterior gnathopoda small, sub- 

 cheliform in both sexes, propodus with distinctly defined palmar 

 border. Posterior gnathopoda very dissimilar in two sexes, in 

 female about as in Talitrus, in male very strongly developed, 

 terminating with very large and powerful subcheliform hand. 

 Perasopoda about as in Talitrus, but last pair somewhat more 

 elongated, and often peculiarly modified in male. Branchial 

 lamellae small. Incubatory lamellae of same structure as in 

 Talitrus, but considerably larger. Appendages of metasome and 

 urosome almost as in Talitrus. 



Species numerous, mostly terrestrial. I do not know if Or- 

 chestes is the original spelling adopted by Leach. If not, and 

 Orchestia is given, it must be used. Leach uses Orchestia in 

 1815. 



Key to the species. 



a. First antennae not quite reaching tip of penultimate segment of second ; 

 hand of second gnathopods of male with notch near posterior end of 

 palm ; carpus of posterior perseopods in adult male much swollen ; com- 

 mon under masses of seaweed near the shore. agilis 



1 Leach, Edinburgh Encyclop., Am. Ed., 1815, p. 241. 



