REPORT ON THE COPEPODA. 97 



Family II. Cyclopidae, Baird (in part). 



Body elongated, in general outline similar to that of the Calanidae ; anterior antennae 

 of moderate length, rarely longer than the cephalothorax ; those of the males alike on 

 both sides, and geniculated for clasping ; posterior four-jointed, and without a secondary 

 branch. Mandibular and maxillary palps well developed or occasionally rudimentary. 

 Foot-jaws much like those of the Calanidae. First four pairs of feet alike, two-branched, 

 and adapted for swimming only ; fifth pair rudimentary, alike in both sexes. Heart 

 wanting. Eyes of the two sides coalescent in the median line. Ovisacs two. 



The absence of an internal branch of the posterior antenna, the rudimentary character 

 of the fifth foot, alike in both sexes, and, in the male the modification of both right 

 and left anterior antennae, to act as clasping organs, distinguish this Family from those 

 already described, while, from the Harpacticidae it is separated chiefly by the structure of 

 the foot-jaws and first pair of swimming feet. Except the genus Oithona, no members 

 of the Family have been observed in the Challenger gatherings. 



Oithona, Baird, 1843. 



Body much elongated, slender ; head quite distinct from thorax. Anterior antennae 

 long and slender. Mandible-palp elongated, two-branched ; secondary branch composed 

 of several joints. Maxillae stout, and provided with a short two-branched palp. First 

 pair of. foot-jaws long and slender, four-jointed (not unlike those of Calanus) ; second 

 pair also as in Calanus, but indistinctly jointed. All the branches of the first four 

 pairs of feet are three-jointed; fifth pair rudimentary, bearing two small setiferous 

 papillae. 



This genus partakes of the characters both of the Cyclopidae and Calanidae, and is 

 perhaps in general appearance more like Acartia (Dias) than any other genus ; in this 

 situation it was placed by Dana. But inasmuch as some of the most important features 

 of the Cyclopidae are present in Oithona, it seems best to consider it as belonging to that 

 Family. The geniculated form of both anterior antennae in the male, the absence of a 

 secondary branch in the posterior antennae, the very rudimentary form of the fifth 

 pair of feet, and the presence of two ovisacs, are all characters in which it agrees with 

 Cyclops. The structure of the internal organs also conforms to that of Cyclops. 



Oithona challengerii, n. sp. (PI. XL. figs. 1-10). 



Length, 1-1 4th of an inch (T8 mm.). Cephalothorax narrow, tapered towards the 

 anterior extremity, and produced into a curved beak (fig. 2) ; abdomen nearly as long as 



(ZOOL. CHALL. EXP. PART XXIII. 1883.) Z 13 



