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



bearing long, plumose apical setse ; the secondary branch usually much shorter, and shew- 

 ing an elongated basal joint, with four incompletely separated median joints. Not less 

 interesting is the form of the mandibles, the biting part of which is very slender, almost 

 stylet-shaped, and terminates in two long, sharp teeth ; the palp consists of an elongated 

 peduncle, with two well-developed branches. . . . The maxillse, instead of having as in 

 Calanus a short lappet-like appendage, show an elongated rod-like process, bearing at its 

 apex two excessively long and usually plumose seta?. ... The fifth pair of feet of the 

 male differ from those of the female in the conversion of the extremity into a prehensile 

 organ ; the outer branch of both feet is destitute of setse, but has at the apex a claw, and 

 the foot of the right side differs still further in having its penultimate joint excavated 

 on the inner border, while the last joint has its marginal spine much enlarged and turned 

 inwards." 



That Claus should have found five species of Hemicalanus in the Mediterranean seems 

 very remarkable, inasmuch as three forms only were noticed in the Challenger gatherings 

 which passed through my hands, and they were represented only by about half-a-dozen 

 specimens in all. 



1. Hemicalanus longicornis, Claus (PI. IX. figs. 1-7). 



Hemicalanus longicornis, Claus, Die frei lebenden Copepoden, p. 179, pi. xxix. fig. ]. 



Length, 1-1 Oth of an inch (2 # 5 mm.). Forehead short and broad, subtriangular; 

 anterior antennas twice as long as the body, very slender beyond the middle, plentifully 

 provided with very long setse (fig. l). Posterior antennas (fig. 2) very long and slender, 

 secondary branch very small, six-jointed, reaching to the end of the second joint of the 

 larger branch ; the small intercalated joints very indistinct, four or five in number. 

 The five pairs of swimming feet all nearly alike ; inner branches only about one-half as 

 long as the outer. Abdomen short, about one-fifth of the length of the body ; caudal 

 st}dets twice or thrice as long as broad ; setse five, nearly equal, not longer than the 

 abdomen. Branches of the mandible-palp (fig. 3) slender, the outer branch two-, the inner 

 one-jointed. 



Habitat.— South Pacific, lat. 40° 3' S., long. 132° 58' W. (Station 288), and North 

 Atlantic in lat. 26° 2l'N., long. 33° 37' W., taken in the tow-net down to 80 fathoms 

 (Station 353). The last-named locality, it will be seen, is almost in the same latitude, 

 and may be supposed to afford pretty much the same external conditions, as the Sicilian 

 Station, at which the same species w T as found by Dr. Claus. The specimen figured 

 in our plate, though imperfect, is drawn accurately from one of the two found in 

 the above-mentioned gathering. 1 



o o 



1 Except as to the jointing of the posterior antenna?, which was taken from a Pacific specimen. 



