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



rostrum that is nearly as long as the carapace, armed on the frontal crest with a series 

 of twelve small spinules, and on the under surface with six minute teeth, the apex is 

 unequally forked, having a small tooth above and a large one below. There is no 

 tooth over the orbital region, but the first antennal tooth is produced to a short point, 

 and at the base of the second antennas is a sharp tooth, but none is present at the fronto- 

 lateral angle. 



The pleon is more than twice the length of the carapace, measured from the orbit 

 to the extremity of -its dorsal surface, and from the posterior dorsal surface of the 

 carapace to the extremity of the telson. The somites of the pleon are deeper than the 

 lateral walls of the carapace, but they lessen in height after the fourth somite, all of 

 which, including the fifth and sixth, are rounded at the postero-lateral margin. The 

 sixth somite is nearly twice the length of the fifth, and a little longer than the telson, 

 which is narrow and tapers to the extremity. 



The ophthalmopoda are short, the ophthalmus is orbicular, but scarcely larger in 

 diameter than the peduncle, and possesses no ocellus. 



The first pair of antennas is short ; the first joint of the peduncle is about equal in 

 length to the two succeeding, it is excavate on the upper surface to receive the ophthal- 

 mopod, and is furnished with a stylocerite that is broad at the base, sharp pointed, and 

 of great tenuity, reaching quite to the extremity of the joint ; the second and third joints 

 are short, the last, which is the shortest, supports two multiarticulate flagella, that are 

 unequal in diameter, the outer being the larger, and neither longer than the peduncle. 



The second pair of antennas is about two-thirds the length of the animal, and carries 

 a scaphocerite that is rounded at the extremity, and armed at the outer angle with a 

 sharp tooth that reaches beyond the end of the scaphocerite, and is subequal with the 

 length of the rostrum. 



The mandible (fig. 3d) has the molar process and cutting margin of the psalistoma 

 continuous and serrate. The molar process is thick, and the psalistoma thin, and at their 

 base a two-jointed synaphipod originates. 



The other oral appendages have not been examined. 



The second pair of gnathopoda (fig. 3i) is pediform, five-jointed and slender; 

 the coxa supports a sharp and rigid tooth that I take to be the rudiment of a mastigo- 

 branchial appendage, and a small arthrobranchial plume ; the basis is short, and supports 

 a long and slender ecphysis, that is nearly as long as the appendage to which it belongs. 

 The next joint is long, and probably represents the ischium and meros united ; the carpos 

 is half the length of the preceding joint, and is greater in diameter distally than at the 

 meral extremity ; the propodos is long, slender, and bluntly pointed, and fringed with 

 long hairs, as is also the carpos and meros on the inner margin. 



The first pair of pereiopoda is a little longer than the second pair of gnathopoda. It 

 is slender and chelate ; the ischium and meros are united by an overlapping articulation ; 



