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



anteriorly. The four succeeding somites are subequal and similar. They are much 

 lunger than the first, and are laterally supported by large coxal plates produced both 

 anteriorly and posteriorly beyond the extremities of their respective somites, and 

 rounded at their posterior and inferior angles. 



The sixth somite is rather shorter and less deep laterally than the preceding, and 

 converges dorsally towards the posterior extremity, where it supports a broad, flat telson, 

 quadrate in form, serrate at the sides by a few sharp, small teeth, and armed with two 

 on the dorsal surface on each side of the median line, and fringed along the posterior 

 margin with a row of deeply-implanted plumose cilia. 



The eyes are small ; the ophthalmopoda conical, broad based, extending to about one- 

 half the length of the rostrum. 



The peduncle of the first pah' of antennae is cylindrical, and reaches a little beyond 

 the extremity of the rostrum. The first joint extends beyond the eye, and has the 

 upper surface slightly excavated to receive that organ. The second is shorter than the 

 hist, and the third is longer than the second. This last joint siqyports two sub- 

 equally long multiarticulate slender flagella, of which the primary or upper branch 

 is rather the shorter and the more robust; one or two long cilia originate from the 

 extremity of each articulus. 



The peduncle of the second pair of antennae reaches beyond the extremity of the 

 peduncle of the first, to an extent equal in length to the last joint of the second pair. 

 There is neither spine nor scale attached to the base of this appendage, and therein 

 it differs fundamentally from the genus Axius of Leach, which is described as having a 

 movable spine. 1 The phymacerite is large, and directed inwards towards the anterior 

 part of the metope, which recedes obliquely backwards to the mouth. The terminal 

 joint of the peduncle supports a slender flagellum that is about one-fourth longer than 

 those of the first pair. 



The mandibles are a pair of convex plates, having the inner side concave towards the 

 incisive or psalisiform margin, but towards the base they have a sudden enlargement or 

 molar prominence, against which the synaphipod plays. This synaphipod arises on the 

 anterior margin, near where it articulates with the metope ; it consists of three joints, 

 of which the distal one is the largest in width and proportions ; it folds round the 

 anterior margin of the mandible, and rests between it and the epistoma. 



The first pair of gnathopoda is subpediform, that is, it somewhat resembles a pair of 



1 Leach in his Malac. Brit, says nothing about the scale (scaphocerite), but figures a rigid, sharp point at the upper 

 extremity of the antepenultimate joint of the peduncle of the second antenna 3 , which he describes as "antennae 

 exteriores setace;e corporis fere longitudine." Milne-Edwards (Hist. Nat. des Crust., vol. ii. p. 311), without any 

 illustration, says, " Le pedoncule des antennes externes presente en dessus une petite epine mobile qui represente le 

 grand palpe lamelleux, que nous rencontrerons chez les Salicoques." Desmarest (Consid. des Crust., p. 206) makes no 

 mention of the scale, and copies Leach's figure. Bell (Brit, Stalk-Eyed Crust., p. 227), without figure, says, " External 

 antenna' nearly as long as the body ; the peduncle furnished above with a small movable spine." 



