38 OllCHES'L'IIDiE. 



AMPHIPODA. ORCHESTIIDjE. 



SALTATORIA. 



Genus— ALLORCHESTES, Dana. 



Dana, United States' Expl. Expecl. p. 883. Proc. Amer. Acad. Arts and 

 Sci. ii. p. 206. Amer. Jl. Sci. 2nd ser. viii. p. 136. 



Generic character. — Like Orchestia, but the superior antennae 

 are longer than the peduncle of the inferior. Maxillipedes un- 

 guiculate. Carpus of the second pair of gnathopoda iuferiorly 

 and anteriorly produced. Telson single. 



The superior antennae are at least as long as the 

 peduncle of the inferior. The inferior antennae have 

 the two basal articulations not so closely incorporated 

 with the head as in Orchestia ; they are, moreover, fur- 

 nished with a small olfactory denticle. The mandibles 

 are without any palpiform appendage. The foot-jaws 

 terminate in a sharp point. The two anterior pairs of 

 legs have subchelate hands. Coxae of the fifth pair of 

 legs shorter than those of the fourth. Caudal appen- 

 dages short and robust. 



Dana established this genus for the reception of cer- 

 tain species of Amphipods which had been attributed by 

 authors to various genera. It more nearly resembles 

 Orchestia than any other genus, but is very easily dis- 

 tinguished from it by the length of the superior antennae. 



Upon first consideration, it would seem that this slight 

 difference could scarcely be of sufficient importance to 

 warrant a generic separation. Closer inspection, how- 

 ever, shows that it is associated with some important 

 changes both in the structure and habits of the animals. 



