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



spines. The setae of the anterior antennae are distributed pretty much as in Acartia 

 laxa, but the joints, just above the origin of each seta, are angularly produced in a tooth- 

 like fashion. In the male (PL XXXII. fig. 12) the right anterior antenna is swollen below 

 the middle, but is only indistinctly geniculated. The fifth foot in the male (fig. 15) is 

 angularly bent, the penultimate joint bearing a stout subquadrate marginal process, the 

 last forming a distorted, acuminate claw: in the female (fig. 16) the basal joint is short 

 and broad, with truncated and angular apex, the two terminal setae nearly equal in length, 

 the inner one dilated at the base, the outer much more slender. The abdomen and tail 

 setae do not differ materially from those of Acartia laxa. 



This is very similar to Dana's Acartia limpida, but some parts of the description 

 cannot rightly apply to our species, as, for instance, " caudal stylets longer than twice 

 their diameter," and " one seta of the posterior foot quite long and a little curved, the 

 other less than a fourth as long" ; moreover, the angular or toothed articulations of the 

 anterior antennae are not mentioned as characterising Acartia limpida. 



Habitat. — Abundant in Hilo Harbour, Sandwich Islands (August 1875) ; one or two 

 specimens noted in a gathering from the Philippine Islands, and (?) in the Atlantic, north 

 of Tristan d'Acunha. 



Calanoides, n. gen. 



Cephalothorax six-jointed (in the male the first joint is barely visible), head united 

 with the thorax ; abdomen of the male five- of the female four-jointed. Anterior 

 antennas twenty-four-jointed, nearly alike in both sexes. Branches of the posterior 

 antennae nearly equal in length, inner branch with three small median joints. Mandible- 

 palp well developed, biting portion of the mandible well developed in the female, very 

 feebly or altogether wanting in the male. Maxillae and foot-jaws as in Calanus ; the 

 foot-jaws very small in the male. 1 Five pairs of feet in both sexes ; the inner and outer 

 branches three-jointed throughout, except in the fifth pair of the male, which are very 

 long, prehensde, and in which the inner branches are rudimentary. 



In general appearance, in the structure of the antennae, maxdlae, foot-jaws, and 

 swimming feet, we have here an almost exact agreement with Calanus ; but the absence 

 of mandible proper in the male, and the conformation of the fifth pair of feet in the same 

 sex, are characters which ally the genus to Euclmta, under which I was at one time 

 disposed to place the single species known to me. Some of the most conspicuous 

 characters of Euchceta are however wanting, as, for instance, the single long caudal 

 seta, and the large doubly flexed posterior foot-jaws ; while the three-jointed inner 



1 In the two or three males which I dissected I was unable, except in one instance, to find any trace of the 

 mandible proper ; in one case, however, I observed a process, not unlike that figured by Giesbrecht as belonging to 

 the male Lucullus acuspes, and which may possibly represent the mandible. 



