122 CARL BOVALLIUS, THE OXYCEPHALIDS. 



tion contained no characteristics of use for the specific distinction. He 

 asserted further that only the fifth and sixth pairs of pereeopoda were pro- 

 vided with branchial vesicles, while, as I have shown above, the second, 

 third, and fourth pairs also have such appendages, but as they are 

 usually concealed by the projecting lateral parts of the peraeonal seg- 

 ments, i. e. the coalesced epimerals, they may easily escape notice. 



In 1887 I gave a short diagnosis of Rhabdonectes armatus, H. 

 MILNE EDWARDS, with characteristics fully sufficient to distinguish it 

 from R. Whitei. 



Among the ))Challenger specimens of Xiphocephalids there seem 

 to be none belonging to the present species. 



The body is much compressed, and is only a little broader in 

 the female than in the male. The integument is very thin, but hard, 

 almost vitreous, and perfectly smooth. 



The head, without the rostrum, is not fully as long as the pereeon. 

 The neck is about a fourth part longer than the ocular region. The 

 rostrum is four or five times longer than the rest of the head, needle- 

 shaped, with two marginal, serrated ridges on the under side; the apex 

 of the rostrum is sharp-pointed. The rostrum is rather longer in the 

 adult female than in the male. The an term al groove is large in the male, 

 forming a protruding convexity in front of the ocular region; in the female 

 it is less spacious, and is not visible on the dorsal side of the head. 



The first pair of antennce in the male (PL VI, fig. 3) are like 

 that pair in Oxycephalidce, having the second and third pedunclar joints 

 almost fused and the last three joints of the flagellum together not half 

 as long as the under margin of the first flagellar joint. In the young- 

 male the first pair are very like that in the young of Oxycephalus 

 piscator. In the female this pair (PL VI, fig. 4) consist of a two-jointed 

 peduncle, and a long single flagellar joint, which is almost spindle-shaped, 

 and set with long olfactory hairs. The second pair in the adult male 

 reach, when folded, to the front wall of the antennal groove; the joints 

 are straight, and have the under margin fringed with short hairs. 



The mandibles are comparatively small, and want a molar tubercle; 

 trie mandibular palp in the male is very long, its first joint being a little 

 longer than the first joint of the second pair of antennas; the second 

 and third joints ave very short, subequal in length. 



