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



The carapace, measuring from the extremity of the rostrum to the posterior margin 

 of the central dorsal surface, is rather more than one-third of the entire length of the 

 animal. The rostrum is dorsally flat and projects as far as the distal extremity of the 

 second joint of the first pair of antennae, the extremity is pointed and curved upwards, and 

 the lateral margins are fringed with hairs and a few (four) short, sharp teeth on each side. 

 The carapace is divided near the centre by a deep cervical sulcus, and the lateral walls 

 are almost perpendicular, and cover and protect the entire branchial apparatus. 



The first somite of the pleon is large and divided into an anterior and a posterior 

 portion. The anterior is smooth, and when the animal is fully extended passes beneath 

 the carapace ; the posterior is also smooth but somewhat elevated, and increases at the 

 lateral margins to a ridge that defines the limit between the somite and the coxal 

 plate, which is associated with it ; this ridge projects forwards into a small process, or 

 pleocleis, that overrides and assists in keeping the posterior margin of the carapace in 

 position. A line of hairs which fringes the posterior margin of the carapace dies out 

 where the lateral process projects, and commences at the corresponding point on the 

 anterior margin and traverses that of the coxal plate of the first somite of the pleon. 



The second somite is dorsally quadrate, but is a little broader at the posterior margin 

 than at the anterior, the lateral crests are well defined and denticulate, the coxal plate is 

 perpendicular, and the infero-lateral margin rounded at the anterior and posterior angles, 

 smooth on the outer surface, but fringed with a row of thickly-set hairs on the inner. 



The third somite resembles the previous one, except that instead of being smooth it 

 is extensively covered with thick, short hairs. The lateral crests or ridges are smooth, 

 the small denticulations on the previous somite being but feebly represented. 



The fourth resembles the third, but is slightly broader, and equals the breadth of the 

 carapace ; the coxal plates, instead of being smooth, are thickly covered with hair on the 

 outer surface towards the postero-inferior angle. 



The fifth somite is somewhat narrower than the. fourth, and is slightly broader at the 

 posterior than at the anterior margin. The dorsal surface is smooth, and the coxal plate has 

 a tendency to turn oblicpiely outwards, and lias a brush of hair at the postero-inferior surface. 



The sixth somite is quadrate, but longer and narrower than the fifth. The coxal 

 plate is less deep than the preceding, and narrows posteriorly. 



The seventh somite or telson is square, flat, and posteriorly fringed with a row of 

 closely-planted hairs. 



The eyes are absent. The metope is smooth, polished, and submenibranous. Two 

 small but prominent tubercles tipped with hairs stand on each side of the median line, 

 and above where the eye should have been the margin of the carapace is slightly excavated 

 to form an orbit. 



The first pair of antennas consists of a three-jointed peduncle and two long sub- 

 equal flagella. The first or coxal joint is longer and larger than the two succeeding, and 



