REPORT ON THE COPEPODA. 43 



Hemicalanus, Claus. 

 Hemicalanus, Claus, Die frei lebenden Copepoden, 1863 (not Hemicalanus of Dana). 



Body pellucid, somewhat depressed, eyes entirely wanting (?). Anterior antennae 

 twenty-five jointed, that of the left side in the male slightly geniculated. Posterior 

 antennae elongated, secondary branch five or six-jointed, the median joints minute and 

 sometimes not distinctly separate. Mandibles almost styliform, two-toothed. Anterior 

 pair of foot-jaws elongated, posterior still longer, robust. Fifth pair of feet two-branched, 

 those of the female like the preceding pairs, as also those of the male, 1 except that the 

 outer branch is uncinate. Abdomen short, composed in the male of five, in the female of 

 four segments. 



Of this remarkable genus I have seen but few examples, most of which were very 

 imperfect. The foregoing definition is therefore copied almost verbatim from Dr. Claus, 

 though in some points it does not quite agree with my own observation, to which, 

 however, I cannot in this case allow much weight. In the best of the Challenger 

 specimens (figured in PL IX. fig. 1) there were two small closely-approximated spots on 

 the front of the head, which I took to be eyes, and I was unable, except in one specimen, 

 to make out more than two joints in the secondary branch of the posterior antenna. The 

 joints of the anterior antennae were also very indistinctly visible, and those organs, as 

 shown in fig. 1, are evidently imperfect. 



The genus as originally constituted by Dana contains species probably belonging to 

 two or more genera, and is certainly in that form untenable. It is impossible, indeed, 

 from the insufficiency of the published characters, to say with certainty where the species 

 assigned to it should properly be placed. None of them can be referred to Hemicalanus 

 as understood by Claus, and upon which he makes the following remarks : 2 — " This genus, 

 of which five species are known to me — on account of its delicate structure, the trans- 

 parency of its body, and its several peculiarities of organisation — ranks amongst the 

 most beautiful and interesting of all the Calanidse. The entire body is extremely slender, 

 like that of Calanella (Eucalanus), but broader and flatter; the abdomen is smaller and 

 more slender but completely segmented, composed in the female of four, or rarely three, 

 and in the male of five segments ; the last segment, bearing the furca, is broad, and often 

 produced, fan-like at the sides. In the species known to me, the cephalothorax is 

 composed of four segments only, the head and first thoracic, as well as the two hindmost 

 segments of the body, being coalescent. . . . The male antenna is hinged between the 

 nineteenth and twentieth joints, but there is no marked swelling of the foregoing joints. 

 The posterior antennae are largely developed, the main branch of great length, and 



1 I cannot reconcile this statement of Dr. Claus with my observation of the fifth pair of feet in the Challenger 

 specimen, which were as represented in fig. 1. 



- Die frei lebenden Copepoden, p. 177. The translation here given is an abstract only of the more important parts. 



