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



about twice as long as the former, whereas in the female (PL XX. fig. l) the difference in 

 h-nsith between the two divisions is much less. 



The carapace lacks every trace of lateral denticles, the inferior margins being quite 

 smooth and nearly straight. The anterior part is marked off posteriorly by a slight 

 cervical impression, and exhibits above a distinct, though somewhat low keel. The 

 frontal margin juts out in the middle (see PI. XX. fig. .3 ; PI. XXI. fig. 2) as a compara- 

 tively short triangular projection, reaching but very little beyond the ocular segment, 

 forming, too, on either side, above the eyes, an obtuse angle. The antero-lateral corners of 

 the carapace constitute a distinctly projecting angle. Posteriorly, the carapace exhibits 

 a rather deep emargination (see PI. XXI. fig. 3), from which juts on either side a narrow 

 sinus, disrupting the hinder margin. 



The caudal segments are all nearly uniform in length, but diminish hindwards succes- 

 sively both in breadth and height. The two foremost have the posterior margin very 

 slightly produced above in the middle, but, in other respects, these segments are quite 

 smooth above. The epimera are of moderate size and somewhat triangular in form, 

 pointing obliquely backward and terminating in an acute angle. The last segment is 

 relatively very short, its length not exceeding that of the preceding, and wants the 

 slighest trace of a preanal spine. 



The eyes (see PI. XX. fig. 2 ; PI. XXI. fig. 2) are very large, projecting towards either 

 side, pyriform, with the cornea greatly expanded. 



The antennular peduncle is somewhat different in the two sexes. In the female 

 (PI. XX. figs. 4-6) it is exceedingly slender, and scarcely exceeds half the length of 

 the carapace, whereas in the male (see PL XXI. figs. 1, 2) it is much more powerfully 

 developed, attaining almost the whole length of the carapace. The basal joint is somewhat 

 flattened, and projects at the outer corner as a sharp tooth. The dorsal leaflet, springing, 

 above, from the end of this joint, is reflexed, as in the northern species, but compara- 

 tively more simple in structure, having only the inner corner acutely produced, whereas 

 the edges are evenly curved and quite smooth. The second joint is very elongate, 

 attaining almost the length of the basal joint, and, in the female, very narrow and 

 perfectly cylindrical in form, whereas in the male (see PL XXL fig. 2) it is much thicker, 

 and exhibits at the inner edge, near the apex, an obtuse prominence that lies in close 

 contact with the corresponding prominence on the opposite side, when the peduncles are 

 extended in their normal position. The last joint is only half as large as the former, and 

 in the male remarkably dilated and somewhat curved. The flagella are very elongate, 

 and composed of numerous short articulations. 



The antennal scale (see PL XX. fig. 7) is comparatively small, not nearly reaching 

 the end of the second joint of the antennular peduncle, and exhibits a rather narrow, 

 nearly linear form, tapering slightly, however, toward the apex, which is narrowly 

 truncate, with the outer corner produced as a well-defined tooth. The basal spine is very 



