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



all attenuated, distinctly separated from the thorax, and constricted at the point of 

 junction. Anterior antennae somewhat longer than the body of the animal, twenty-four 

 jointed, clothed with very short setae, two or three on each joint, and with a single, 

 rather longer, rigid seta at the apex of the second, third, eighth, thirteenth, fifteenth, 

 and seventeenth joints ; the last two joints bear a lash of setae of moderate length ; in 

 the male the antenna! joints are constricted at the bases. Posterior antennae slightly 

 different in the two sexes, as in Eucalanus attenuatus (figs. 9, 10). Basal joint of the. 

 mandible-palp (fig. 11) short and broad, outer branch composed of only one joint, inner 

 branch small and two-jointed. Maxillae and foot-jaws asin Eucalanus attenuatus. The 

 swimming feet (fig. 12) have no terminal spines; all the inner branches are two-jointed, 

 except those of the first pair, which are one-jointed (?). Those of the fifth pair of the male 

 are very slender (fig. 13), simple, and composed of five joints, the last of which is small 

 and setiform. The last two thoracic segments bear each a slender, divaricate lateral seta 

 (fig. 14). The abdomen of the female is extremely short and three-jointed, that of the 

 male (fig. 15) four-jointed. 



Habitat. — Between Sydney and Wellington ; Arafura Sea ; off Sibrabo Island and 

 Zebu Harbour, and at two other stations {circa 201, 202) amongst the Philippine Islands ; 

 off St. Vincent Islands, Cape Verde; in lat. 7° 33' N., long. 15° 16' W. (Station 350) ; 

 and in lat. 34° 37' N., long. 140° 32' E. (east of Japan, Station 237). 



In general appearance this is deceptively like the male Calanus Jinmarchicus, and 

 affords a remarkable instance of homomorphism — perhaps even of mimetic resemblance — 

 between two certainly distinct genera. I do not remember to have seen amongst the 

 Calanidae any other so well marked example of this condition. Without minute 

 examination, the only palpably distinctive character is the somewhat greater length of 

 the antennae of Eucalanus. The two genera, however, differ essentially in the structure 

 of the posterior antennae and the fifth pair of feet. 



Rhincalanus, Dana. 



Animal slender and elongated, cephalothorax many times as long as the abdomen ; 

 head and thorax coalescent, five-jointed ; anterior part of the head produced. Anterior 

 antennae abke in both sexes, much longer than the body, bearing numerous short and a 

 few very long setae ; inner branch of the posterior antennae multiarticulate, the last five, 

 joints very short and nearly equal. Mandibles broad and strongly toothed at the apex ; 

 palp well developed, with a large basal joint and two branches, one composed of two, the 

 other of three joints. Maxillae and foot-jaws nearly as in Calanus. Swimming feet, five 

 pairs, short ; inner branches of the first four pairs small and three-jointed, except in the 

 first pair, which has only two joints; fifth pair one or two-branched. Abdomen four- 

 jointed. 



