10 R. NORRIS WOLFENDEN. 



2. CALANUS ACUTUS. 

 (Plate I., figs. 9, 10.) 

 Calanus acutus, Giesbrecht, ' Belgica ' Report,* p. 17. 



This copepod was first described by Giesbrecht from the Belgian South Polar 

 Expedition, and in the ' Discovery ' collection it forms the chief constituent of the South 

 Polar copepod plankton, along with Euchceta antarctica. 



The majority of the animals I have met with both in the ' Gauss ' and ' Discovery ' 

 collections are smaller than the size given by Giesbrecht, viz., 4 '7-5 '3 mm. But few 

 of our specimens reach 5 mm. length, the majority being from 4 '5-4 '7 mm. The 

 cephalothorax is not quite four times as long as the abdomen, the head divided from 

 the first thoracic segment, the last segment of the latter produced laterally, but with 

 evenly rounded margins and no points. In lateral aspect the head is slightly 

 produced forwards, and more inclined to be oval than rounded. In the dorsal aspect it 

 has a distinct triangular appearance, with slight crest in the mid-line. In its broadest 

 part the thorax is 1 15 mm. broad, that is, three times as long as broad. 



The furcal segments are a very little longer than the anal, and nearly twice as long 

 as broad. The anterior antennae vary in length in different animals, in some being only 

 as long as the furca, in others one or two joints longer, and are distinguished by the 

 comparative length of the last joint, which is about twice as long as the one before it. 



In the second feet the Re is divided into two portions, proximal = 24 ; distal =13. 

 third = 29; =15. 



fourth ,, = 15 ; ,, = 15. 



The Ri 3 has in the second and third feet eight bristles, in the fourth only seven, 

 and in the fifth only four (with no outer marginal bristle). The end saw of the Re 3 of 

 the second feet is shorter than the Re 3 ; in the third and fourth pair longer. 



The fifth feet are distinguished by the absence of the outer marginal bristle of the 

 Ri 3, and the total absence of teeth or hairs on the inner margin of the first basal. All 

 males appeared to be immature. 



3. CALANDS SIMILLIMUS. 



(Plate I., figs. 5, 6.) 

 Calanus simillimus, Giesbrecht, ' Belgica' Report, p. 17. 



$ 2 '5-2 '9 mm. ; cephalothorax, 1*9 mm. ; abdomen, '6 mm. long. 

 Head separate from first thoracic segment, evenly rounded, without any trace of 

 crest. Head not quite as long as the rest of the thorax (as 18 :21). Last thoracic 



* " Belgica Report " is throughout this monograph used to indicate " Rsultats du Voyage du S. Y. ' Belgica ' 

 en 1897-1898-1899." Rapports Scientifiques. 1902. 



