42 THE 70YAGE OF H.M.S. CHALLENGER. 



figured in the cephalothorax and abd n differs in the two specimens represented in the 



plate (figs. 1 and 2). These were drawn as they appeared under the microscope. The 

 differences may perhaps be sexual, but of this I could find no evidence. 



Habitat. — Off Sibrabo Island, and in several other localities amongst the Philippine 

 Islands; and in lat. 5° 28' N., long. 14° 38' W. (Station 349). Dana's specimens were 

 collected in the Sulu Archipelago. 



2. Rhincalanus gigas, n. sp. (PL VIII. figs. 1-11). 



Female. — Length of the body one-third to three-eighths of an inch (8*5-10 mm.). 

 Anterior antennas twenty-three-jointed, nearly as in Rhincalanus cornutus, but with some- 

 what shorter marginal setse. Forehead not so much elongated as that of Rhincalanus cor- 

 nutus. Ventral angles of the last three thoracic segments produced into overlapping spines. 

 Abdomen composed of four segments, the first and last of which form spinous processes at 

 their postero-dorsal angles. The inner branches of the swimming feet are three-jointed, the 

 outer branches very feebly spinous, the spines, as in Rhincalanus cornutus, being merely 

 small, unjointed processes of the limb, in the last joint amounting to little more than 

 marginal crenulations (fig. 8). The feet of the fifth pair (figs. 9, 10) are one or two 

 (?) branched, the terminal joint bearing three, the penultimate joint one apical seta. 

 Caudal stylets about as long as broad, setae subequal (fig. 11). 



Habitat. — Rhincalanus gigas, though distributed over a very wide area, seems to be 

 much more abundant in the southern hemisphere than in more northern latitudes. The 

 following Hst indicates the localities in which it was taken by the surface-net during 

 the cruise of the Challenger : —In lat. 65° 42' S., long. 79° 49' E., 80 fathoms (Station 

 153); lat. 64° 37' S., long. 85° 49' E. (Station 154) ; lat, 47° 25' S., long. 130° 32' E. 

 (Station 159); near Station 206, January 9, 1875; lat. 37° 17' S., long. 53'° 52' W. 

 (Station 320); lat. 36° 44' S., long. 46° 16' W. (Station 325) ; and between Japan and 

 Honolulu. 



This species differs from Rhincalanus cornutus chiefly in size, being more than twice as 

 long; also in the less attenuated forehead, in the situation of the thoracic spines (which are 

 on the ventral surfaces of the somites instead of on the dorsal), and in the characters of the 

 fifth pair of feet. Fig. 9 in the plate represents, I believe, the normal form of that limb, 

 but in another specimen it was found as in fig. 10. No perfect anterior antennas were seen, 

 but those shown in the figure are probably nearly, if not quite, correct. The terminal 

 spines of the swimming feet are very slender and scarcely distinguishable from the 

 marginal setas. The specimens here described are probably females, in which case the 

 male has yet to be discovered. 



