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



laterally compressed tooth. The next two are similar but have no transverse groove ; 

 the dorsal ridge becomes slightly carinated, and this carina extends to the extremity of 

 the sixth somite, but is not produced to a tooth. 



The telson is long and laterally compressed, terminating in a sharp-pointed 

 extremity, and reaching as far as the distal extremity of the inner branch of the tail- 

 fan ; it is smooth and slightly flattened on the dorsal surface, depressed at the margins, 

 which are armed with four, unequally distant, small, movable spines, the anterior of 

 which is near the middle of the margin. 



The ophthalmopod is flattened and has the rudiment of a tubercle on the inner 

 margin. The ophthalmus is orbicular and a Httle broader than the diameter of the stalk. 



The first pair of antennae has the peduncle about half the length of the rostrum. 

 The first joint is a little longer than the ophthalmopod, and is flattened, but not 

 deeply excavated, for its reception, and has only the rudiment of a prosartema on the 

 inner side, while on the outer the stylocerite longitudinally overlaps the margin and pro- 

 jects beyond the anterior outer angle as far forwards as the distal extremity of the 

 second joint, which is subcylindrical, and rather more than half the length of the first ; 

 the third is short and carries the smaller flagellum about midway between the base and 

 the distal extremity, where the longer flagellum articulates ; the shorter flagellum is 

 about half the length of the peduncle, while the longer one is equal to the entire length 

 of the animal. 



The second pair of antennae has all the five joints of the peduncle freely articulating 

 one with the other ; the coxal joint carries on the inner side a prominent phymacerite, 

 the membranous surface of which is directed obliquely forwards and inwards. The 

 second carries, on the upper and outer side, a large foliaceous scaphocerite, strengthened 

 on the outer margin by a longitudinal ridge that terminates in a sharp tooth one-fifth from 

 the distal extremity, and supporting, on the inner and upper margin, a small hook-like 

 process, which, when at rest, is lodged in a hollow on the under surface of the first joint 

 of the first antenna, just within the rigid base of the stylocerite ; the third joint articulates 

 longitudinally with the second on the inner side, the fourth joint is short, and the fifth 

 reaches to nearly half the length of the scaphocerite, and terminates in a long and 

 slender flagellum that is about once and a half as long as the animal. The epistoma is 

 narrow, and projects in the form of a small rostrum ; the cheiloglossa is prominent, 

 triangulate, rigid anteriorly, and forming on each side posteriorly a large tubercular 

 process that corresponds with, and occupies, the depression between the psalisiform and 

 molar processes. 



The mandibles are strong and powerful, and carry a two-jointed synaphipod, the 

 first joint of which is long and narrow and the second short and triangulate, and both 

 are thickly studded with hairs. The psalistoma is smooth, except for a single small 

 denticle near the centre ; it is sharp-pointed at the anterior angle, and overlaps its fellow. 



