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



somite is the most prominent, while on the sixth somite the larger tooth is represented by a 

 number of small denticles, a condition that is repeated to a less extent on the anterior 

 surface of the telson. At the lateral margins of the several somites, and fused with 

 them, is a large flat coxal plate, of which 'that of the second is the largest, and the pro- 

 portions gradually diminish to the sixth, while that of the first somite is either absent 

 or reduced to a minimum. 



The first somite of the pleon is not so wide as to reach to the lateral margins of the 

 carapace, but the extremities are directed forwards and overlap the posterior margin, 

 from which a strong cusp is posteriorly produced and rests upon the upper surface of 

 the posterior division of this somite, on the inner side of which is a second cusp or tooth. 

 Thus we find that the lateral extremity of the somite keeps down the margin of the 

 carapace, whereas a cusp of the latter presses down the surface of the somite, each 

 retaining the other in its place by a specially-formed cusp or bolt (the pelteeleis). A 

 corresponding cusp exists on the posterior margin of the somite articulating with a 

 smaller one on the anterior margin of the second somite, in a limited ball and socket 

 articulation, and this is repeated on each somite successively. 



The ophthalmopod is fixed in a long and narrow orbit in the frontal margin of the 

 carapace, and carries a tooth on the anterior surface, from which it suddenly narrows 

 laterally, becoming depressed so as to pass beneath the latero-anterior angle of the 

 carapace, which is produced anteriorly, and elevated to the plane of the dorsal surface 

 of the carapace, and so passes over the eye and protects it. The ophthalmopod appears 

 to be firmly united to the carapace at the inner margin of the orbit, but not on the 

 outer, against which it is closely compressed, passing through a cavity on the under 

 side, formed by the frontal region folding back against the antenna! Here it appears 

 small and pointed, and the lens, I presume, exists in the extremity beneath a semi- 

 translucent cornea, protected and almost hidden by a. mass of hairs. 



The first pair of antennad has the inner process of the first joint of the peduncle 

 anteriorly pointed ; the margin is but slightly curved upwards, thickly fringed with 

 ciliated hairs and armed with two small teeth, as also is the outer margin, as well as that 

 of the second and third joints; on the outer distal angle are two strong teeth, one before, 

 the other behind the auditory fissure (fig. 3c). The under surface is at right angles with 

 the inner, and is hollowed to receive the extremity of the phymacerite. The second joint 

 is short and cylindrical, and the third, still shorter, supports one long and one short 

 flagellum. The articuli of the inner flagellum are long and slender, and sparsely ciliated; 

 those of the outer are short and thickly ciliated. 



The second pair of antennae has the first joint or coxa articulating freely with the 

 metope, and on the under surface supports a long phymacerite, the extremity of which 

 turns upwards and impinges against a depression on the inferior surface of the coxal 

 joint of the first antenna. The orifice is therefore curved upwards, and is covered by a 



