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



jEtidius armatus, n. sp. (PI. X. figs. 5-16). 



Length, l-12th of an inch (2'1 mm.). Front of the head very broadly rounded, 

 rostrum very stout, cleft to the base and produced in a continuous curve from the fore- 

 head. Last thoracic segment much produced, composed apparently of two fused somites, 

 and forming at each side a backward-pointing spine, which is as long as the first 

 abdominal segment. Anterior antennae twenty-four-jointed (fig. 6), about as long as the 

 body, the eighth joint longer than those which immediately precede and follow it ; the 

 joints from the fifteenth onwards are longer and more slender than the rest, except the 

 last, which is very small ; all the joints bear setae, most of which are small, and none of 

 excessive length. The two branches of the posterior antennae (fig. 7) are nearly equal, 

 and the inner branch has four very small median joints. The basal joint of the mandible- 

 palp (fig. 8) is large, the two branches small and indistinctly two- and three-jointed. 

 Maxillae and both pairs of foot-jaws (figs. 9, 10) small, and like those of Calanus. The 

 inner branch of the second foot shows an indistinct division near the base (fig. 12) into 

 two joints ; those of the third and fourth pairs are distinctly three-jointed (figs. 13, 14), 

 but the first joint is in both cases very small. The fifth pair of the male (fig. 15) is 

 almost obsolete, the outer branch composed of three, the inner of only one joint, and 

 entirely destitute of setae. Caudal segments about twice as long as broad, setae nearly 

 equal, and as long as the abdomen. 



Habitat. — Indian Ocean in lat. 46° 46' S., long. 45° 31' E. (Station 146) ; in Torres 

 Straits, off Port Jackson, at night; Chinese Sea, in lat. 17° 54' N., long. 117° 14' E. 

 (Station 206) ; in lat. 32° 24' S., long. 13° 5' W. (Station 335); and in lat. 3° 10' N., long. 

 14° 51' W. (Station 348). 



The strong curved rostrum, and the remarkably elongated, spiniform, posterior thoracic 

 segment distinguish this species at a glance from any other with which I am ac- 

 quainted. 



Drepanopus, 1 n. gen. 



Head and thorax coalescent. Anterior antennae twenty-three-, twenty -four-, or-twenty- 

 five- jointed, nearly alike in both sexes. Posterior antennae and mouth-organs as in 

 Calanus. Inner branches of first pair of feet one-jointed ; of the second pair one- or two- 

 jointed; of third and fourth pairs three-jointed. Fifth pair in the female rudimentary, 

 composed of one branch only, in the male two-branched, prehensile, dissimilar on the two 

 sides ; inner branch rudimentary. Abdomen of the male five- of the female four-jointed. 



The number of joints in the swimming feet here corresponds with that of the preceding 

 genus, JEtidius, but the presence of a fifth pair in the female, and the prehensile 



1 l/iivituoii, a sickle ; irois, a foot. 



