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



the Challenger gatherings, fifty-eight belong to the Calanidse. On the other hand, there 

 can be little doubt that had it formed part of the plan of the expedition to investigate 

 fully the littoral fauna of the countries visited, we should have found the proportionate 

 number of species reversed for that zone in favour of the Harpacticidse. The Calanidae, 

 indeed, by virtue of their enormously-developed anterior antennae (often equalling, or 

 more than equalling, in length the entire body of the animal), are specially adapted for 

 an entirely natatory life, those organs when spread out at right angles to the body acting 

 like the wings of a hovering bird, and so suspending the animal at almost perfect rest in 

 the water. In the Harpacticidse, on the contrary, we find antennae usually so short that 

 they can be of very little use as swimming organs, — this function probably devolving 

 almost entirely on the feet. And as a result of this structure, the members of the family 

 haunt chiefly either the muddy sand of the sea-bed, or littoral situations, where there 

 is abundance of weed, on the fronds of which they rest and find their food, swimming 

 only fitfully and by short jerks. 



Following the classification adopted in my Monograph of the British Copepoda, 1 I 

 unite with the Calanidse the species referred by Dr Claus to a separate family, Pontellidse, — 

 distributing the Calanidse under two sub-families,— Calaninse and Pontellinse. 



The fifty-eight species of Calanidse taken by the Challenger belong to the following 

 genera : — Calanus, Eucalanus, Rhincalanus, Hemicalanus, Pleuromma, Heterochceta, 

 Leuchartia, Undina, Scolecithrix, Euchceta, Calanoides, JEtidius, JDrepanopus, Phyllopus, 

 Temora, Centropages, Candace, Acartia, Corynura, Ccdanopia, Pontellopsis, and 

 Pontella. 



Sub-family I. Calaninse, Dana. 



This sub-family is characterised by the presence of only one eye, which is sessile and 

 made up of several lenses. 



Calanus, Leach. 



Calanus, Leach, Diet. Sci. Nat. XIV., Art. Entomostraca (1819); Dana, in part, Crust. U.S. Expl. 



Exped. (1852), Boeck, Oversigt Norges Copepoder (1864); Lubbock passim; Brady, 



Monog. Brit. Copep. (1878). 

 Cetoehilus, Eoussel de Vauzeme, Claus, Baird, Goodsir. 

 Monoculus, Gunner, Act. Hafn. (1765). 



Cephalothorax elongated, slender, composed of five or six segments ; head usually 

 separate from the thorax, and often more or less distinctly divided near the middle by a 

 transverse " cervical suture " ; rostrum attenuated and bifid. Eyes small, situated 

 at the back of the head, near the middle line, each composed of two lenses. Anterior 

 antennae long, composed of twenty-five joints, alike on the right and left sides in both 



1 Bay Society, 1878. 



