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



with the gastric region is a small longitudinal crest which continues to the anterior 

 margin. 



The ophthalmopoda (fig. la) are of moderate proportions, projected on a short stalk 

 or pedicle and furnished with a small marginal ocellus at the posterior surface of the 

 ophthalmus, while at the inner and outer surfaces there is a small tubercle. 



The first pair of antenna? (fig. lb) has the peduncle very short ; the first joint is 

 deeply excavate and carries only a rudimentary stylocerite ; the two succeeding joints 

 are extremely short, and both flagella are long, the inner being very stout at the base, 

 and suddenly narrowing to a slender filament. 



The second pair of antenna? (fig. lc) is remarkable for the peculiar styliform character 

 of the scaphocerite, which is subequal in length with the rostrum ; the outer margin is 

 serrate, and the inner fringed with closely packed hairs to within one-third of the length 

 from the apex ; near the base of the outer margin on the under side is a curved process, 

 and near the hinge another lying parallel to it. On the second joint there is a large 

 sharp-pointed and rigid tooth, at the base of which is a notch or groove upon the upper 

 surface, which corresponds with the small tubercles or curved processes on the under side 

 of the scaphocerite, so that when the latter is thrown outwards these curved processes 

 fall into the notch at the base of the tooth, while the inner shoulder of the scapho- 

 cerite lies under the posteriorly directed antennal tooth, and thus the scaphocerite 

 becomes locked rigidly in a position that makes it a strong bayonet-like weapon of 

 offence. 



The mandibles (fig. id) consist of a concavo-convex psalistoma or incisive plate having 

 a closely serrate margin of regular dentition — the central tooth and the one at the 

 anterior extremity being the largest — terminating with the molar process, into the hollow 

 formed by which the synaphipod falls ; the latter organ is three-jointed, the terminal 

 joint being short, broad, and fringed with hairs. 



The first pair of gnathopoda (fig. Ih) is short and has the terminal joints broad, flat, 

 and reflexed, fringed on the inner side with hairs and stiff spines ; the basis carries a 

 long ecphysis that is flat and fringed with long hairs, and to the coxa is attached a small 

 and almost rudimentary mastigobranchial plate, and a similarly developed podobranchial 

 plume. 



The second pair of gnathopoda (fig. li) is subpediform, having the ischium long, 

 flattened, curved, and fused with the meros, the carpos and propodos subequal, the latter 

 terminating in a point and fringed with soft hairs. The basis is short and carries a long, 

 flat ecphysis. fringed with hairs. The coxa carries a rudimentary mastigobranchial plate 

 that at the anterior extremity is produced to a straight tooth and at the posterior to a 

 curved one. 



The first two pairs of pereiopoda are chelate (fig. Ik), and are remarkable for the 

 fusion of the meros and ischium into one joint, and the shortness of the carpos. The 



