602 THE VOYAGE OF H.M.S. CHALLENGER. 



The side-plates of the perason varying greatly in size, but those of the sixth and 

 seventh segments never very large. 



Pleopods generally having the inner angle of the peduncle armed with two or 

 more small coupling spines, and the first joint of the inner ramus furnished with some 

 apically-cleft spine-like setse. 



Family Okchestid^, Leach, 1814. 



The following is the definition of the family by Boeck, 1872 : — 



" Upper Lip strong, rounded at the apex. 



" Mandibles very strong, curved, much dentate at the apex, carrying a row of 

 plumose spines ; inner appendage strongly dentate ; molar tubercle very prominent ; 

 palp wanting. 



" First Maxillse armed with strong pectinate teeth ; inner plate elongate, narrow, 

 with two plumose setae at the apex ; palp small or wanting. 



" Second Maxillse with broad plates. 



" Maxillipeds with the outer plate small, broad, ovate, having on the margin slender 

 sjDines or setse; the inner plate elongate, broad, apically truncate, armed with three 

 strong teeth ; palp strong and broad, the last joint sometimes wanting. 



" Body compressed ; back rounded ; side plates well developed. 



" Upper Antennee more or less shorter than the lower, without accessory flagellum. 



" Lower Antennse with the two anterior joints very short but pretty broad. 



" Uropods short and strong ; the first and second biramous, the last pair one- 

 branched. 



" Telson short and thick." 



Genus Orchestia, Leach, 1813. 



Leach, in 1813, in the first division of his famil}' Gammarini, defines Talitrus as 

 having "Anterior pair of feet larger than the second jaair; no hands," and Orchestia as 

 having " Two anterior pair furnished with a movable thumb, which is capable of being 

 bent on the edge of the hand ; second pair largest, having a compressed hand." For 

 further definitions, see Notes on Leach, 1815 (p. 90), Friediich Mliller, 1848 (p. 226), 

 J. F. Brandt, 1851 (p. 244), Dana, 1852 (p. 257). Boeck's definition, 1872, includes 

 " Maxillse Imi paris palpo destitutse," but some species of Orchestia, if not all, have a 

 rudimentary palp on the first maxillfe ; it also includes "pedes maxillares palpis per- 

 brevibus latis ; articulo palpi 2do sursum dilatato, 4to absenti," in which statement it 

 would probably be more accurate to substitute rudimentari or tuherculiformi in the place 

 of the word absenti. 



