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



and project posteriorly beneath the coxal plate of the first somite of the pleon. The 

 ophthalmopoda are short, movable, and lodged in a hollow tubercle that is elevated so 

 as to appear almost as if it were the organ it covered, and is armed with a sharp 

 pointed tooth projecting forwards. 



The first pair of antennae (b) has the first joint armed with a sharply pointed 

 stylocerite that is nearly as long as the joint, and on the outer side with short stiff 

 spines. The second joint is narrower than the first, a little longer, and cylindrical, 

 while the third is less than half the length of the second and terminates in two slender 

 flagella. The outer and upper flagellum, which is the stouter, remains thick for a con- 

 siderable distance, and then lessens abruptly, and divides into two, one division being 

 short and truncate and the other continuously slender. 



The second pair of antennas (c) carries on the second joint a long, slender, and 

 sharp tooth that in length nearly equals the scaphocerite, which is also armed with 

 a long and straight spine that reaches to the extremity of the terminal joint of the 

 peduncle, and is separated for nearly half its length from the inner squamiform plate to 

 which it is attached. 



The mandibles (c/) have an evenly serrate, convex, tenuous psalistoma, and a long, 

 cylindrical, robust, molar tubercle, at the base of which a short, broad, thin, two-jointed 

 synaphipod is attached. 



The first pair of siagnopoda (e) is three-branched ; the central branch is broad and 

 spinous at the outer extremity, and smooth on the inner and outer margins ; the inner 

 plate is long, curved, and rigid, and the outer short, obtuse, and membranous ; the two 

 latter are almost free from hairs or cilia. 



The second pair of siagnopoda (_/* ) consists of a short central branch, an inner branch 

 consisting of two plates, and an outer branch, which is produced anteriorly and posteriorly 

 in the form of a scale, the margin of which is fringed with radiating cilia. 



The third pair of siagnopoda (g) approximates to the preceding pah, but 

 differs chiefly in having the mastigobranchial plate separated distinctly from the 

 basecphysis. 



The first pair of gnathopoda (h) is short and of great tenuity. It is seven -jointed, 

 subpediform, and has the terminal joints squamiform, the dactylos, being broad and 

 short, forms a ciliated marginal plate along the anterior portion of the propodos. The 

 basis carries a long and slender ecphysis, and the coxa is furnished with a short trian- 

 gular mastigobranchial plate without a branchia. 



The second pair of gnathopoda ({) is pediform, long, robust, and five-jointed. 

 The coxa carries a small podobranchial plume ; the basis a short and slender ecphysis ; 

 the third joint, which probably represents the ischium and meros combined, is long, 

 curved, and transversely triangulate ; the following joint, which I presume represents 

 the carpos, is short and triangular, and the terminal joint, which represents the propodos 



