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



tubercles viewed from above are irregularly conical, and connected witb tbe vertex by a 

 tumid ridge, which is more distinct in the female ; viewed from below the tubercle points 

 downwards, and the tip extends a little beyond the base of the antenna. Eound the in- 

 sertion of the antenna the tubercle is furnished with a coronet of stiff hairs, curved at the 

 apex. The antennae themselves are at least half the length of the body, and are four- 

 jointed, with two intermediate jointlets (PI. III. fig. 1), one between the second and third 

 joints of the antennae, and one between the third and fourth ; in each case the jointlet 

 belono-s to the joint preceding it. In one species the jointlets are said, but I think 

 erroneously, to be absent.^ 



The first joint is the longest, and often nearly, and sometimes quite, as long as the 

 other three joints taken together ; very narrow at the extreme base, thick above the base, 

 then narrowing to the middle, and often slightly incrassate at the apex ; usually slightly 

 curved ; covered with numerous semi-adpressed haii-s, except at the extreme base ; the 

 apex with stronger and longer hairs. 



The other joints have similar pubescence to the first, except that the fourth has not 

 strono-er hairs at the apex. These joints vary in length and thickness in the various 

 species, but usually the second is gradually incrassate from base to apex ; the third is 

 thicker than the second, and often shorter; and the fourth is generally the thickest 

 of all, sometimes incrassate upwards, and sometimes attenuate from the middle upwards. 

 The jointlets have a finer integument (not furnished with pubescence) than the true joints, 

 and are usually of a paler colour than these. That between the second and third joints 

 is narrow at the base and widens to the apex ; the other is much smaller, and ring-like. 

 In some species the antennae are provided with a few fine spines. 



The Rostrum is four-jointed, and reaches to the front margin of the mesosternum. 

 The labrum is pentagonal, the basal sides oblique, and the apical sides forming a triangle ; 

 it reaches to or beyond the apex of the second joint of the rostrum. 



The first joint of the rostrum is stout, and broader than long. The second is ring-like, 

 and less than one-haK the length of the first. The third is much the longest, stout, 

 widened a little above the base, then diminishing to the apex. The fourth is much shorter 

 than the third, less stout, and triangular in outline. The apex terminates in three short 

 processes, one above and two below (PL III. figs. 2 and 3). The upper process (between 

 which and the rest of the joint is a rather ill-defined transverse suture) is the broadest, 

 and is rounded at the end ; the two under processes are gradually narrowed to the end, 

 which is gently rounded, their inner margins are sub-parallel, and their tips are shortly 

 longitudinally striate. Between them is the end of the furrow in which the mandibles lie. 

 In a line with the inner edges of the two inferior processes the margins of the furrow for 

 the mandibles are longitudinally thickened, and have in the terminal joint of the rostrum 

 a dark spiral line running round each (PL III. fig. 3). This spiral line is not continued into 



1 See the description oi Halobates frauenfeldanus, postea. 



