1468 THE VOYAGE OF H.M.S. CHALLENGER. 



First Gnathopods. — The wrist apically squared rather than produced. 



Second Gnathopods. — The wrist broader as well as much longer than that of the first 

 pair, the hand, when bent against it, not reaching at all beyond the apex of the 

 wrist's process. 



First and Second Perseopods. — The first joint with elongate neck. 



TJiird Pcrmoptods. — Front margin of the first joint not at all serrulate, the fifth joint 

 much shorter than the fourth. 



Fifth Perseopods. — The first joint a little narrowed apically. 



Uropods. — The rami of the first pair are broad, abruptly narrowed distally, the outer 

 ramus rather shorter than the inner (not, as in Spence Bate's description, equal) ; of the 

 second pair the proportions were not ascertained (Spence Bate gives the rami equal). In 

 the third pair the apex of the longer inner ramus reaches beyond the telson as in Claus' 

 figure of Platyscelus armatus. 



Length, sixth-tenths of an inch. 



Locality.— Station 172a, July 22, 1874; off Tongatabu ; lat. 20° 56' S., long. 

 175°11'W. ; 240 fathoms ; surface temperature, 75°. One specimen, female, containing 

 numerous young ones. 



Remarks. — The species is separated from the Mediterranean Platyscelus oroides 

 by details of the third and fourth perseopods, in the third pair the first joint having its 

 front margin almost completely smooth instead of finely serrate, and in the fourth pair 

 the first joint having the slit on the outer surface extremely small instead of tolerably 

 long, its position corresponding with that in Platyscelus armatus. 



The young show some curious differences from the young of Risso's species as figured 

 by Claus. The head corresponds with that described by Spence Bate for the young of 

 his Platyscelus serratus, being long and narrow, tapering anteriorly. The mouth organs 

 bulge, conspicuously on the under side of the head. 



Tlie Upper or Anterior Antennae are situated on the under surface of the head very 

 near the rounded apex, which is folded under ; the first joint thick, longer than broad, 

 the second narrower, not longer than broad, the third much smaller than the second, 

 carrying an apical setule; the first joint of the flagellum nearly as long as the first of the 

 peduncle, with a subapical group of four short filaments, the second joint shorter with 

 four long filaments at the truncate apex, one longer than the other three. 



The Lower Antennae are attached far back, a little above and in front of the base of 

 the mouth organs ; the first joint is rather long, the second and third shorter, these three 

 presumably constituting the peduncle ; the two following joints are much shorter and 

 slenderer, about equal in length, the terminal one tipped with four filaments, the 

 penultimate having a single subapical filament. 



The Gnathopods are peculiar ; the first joint is, as in the adult, the longest, it is 



