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



anterior part has a well-marked keel ruiiuiug along the dorsal face, and juts out as an 

 exceedingly narrow, subulate rostrum, curving gently downward, and reaching almost to 

 the end of the basal joint of the antennulaa (see figs. 8, 9). The antero-lateral corners of 

 the carapace are produced into an acute lobe, overlapping at the side the basal part of the 

 antennte. The posterior emargination is somewhat deep, exposing as usual the dorsal 

 part of the last segment of the trunk. 



The caudal segments diminish successively both in height and breadth posteriorly, 

 and have the epimera distinctly projecting beneath the ventral face, and of a rounded form 

 The antepenultimate and penultimate segments are slightly keeled above, the keel jutting 

 out posteriorly into small dentiform projections. • The last segment is appreciably longer 

 than any of the preceding, and a little compressed, exhibiting a distinct unguiform preanal 

 spine, usually found armed at the base with a small secondary tooth (fig. 7). 



The eyes (see PI. XXIV. fig. 1) are prodigiously developed, and of larger size, perhaps, 

 than in any other known form of Podophthalmia. They are irregularly globose in shape, 

 with the cornea greatly expanded, and, as it were, divided into two sections l)y a well- 

 marked transverse impression running straight across the middle. 



The antennular peduncle (PI. XXIV. fig. 2) is rather slender, and exhibits a structure 

 very simdar to that in the genus Tliysanoessa, the basal joint being rather flattened, 

 whereas the two outer ones are narrow, cylindrical, about equal in length, and, taken 

 together, as long as the basal joint. The anterior l)order of the basal joint projects 

 somewhat above, and has, as in Tliysanoessa, a distinct indentation in the middle, the 

 outer corner jutting out as an acute denticle, whereas the inner is obtuse and provided 

 with two very strong recurved setse. The flagella are, as in Thysanocssa, very short, 

 .scarcely exceeding half the length of the peduncle. 



The antennal scale (fig. 3) exhibits a remarkably narrow, nearly linear form, and 

 reaches almost to the tip of the antennular peduncle ; its apex is very narrowly truncate, 

 with the outer corner projecting as a small tooth, the inner rounded off. The basal spine 

 is very short and cjuite smooth. The flagellum is poorly developed, with the peduncle 

 very narrow and not nearly attaining the length of the scale, the terminal part being some- 

 what shorter than the peduncle, and composed of sixteen to eighteen short articulations. 



The anterior lip (fig. 4) exhibits the usual galeate form, with the lateral angles, 

 however, but slightly produced. 



The posterior lip (fig. 5) has the terminal lobes somewhat expanded and triangular in 

 form, exhibiting exteriorly a distinct and nearly right angle. 



The mandibles (fig. 6) exhibit, as to the form of the body, a perfectly normal appear- 

 ance, the cutting edges (fig. 7) being divided into several sharply pointed teeth. The 

 palp, on the other hand (figs. 6, 8), is remarkably small, not even attaining half the 

 length of the body of the mandible. It is, moreover, very narrow, and but sparingly 

 furnished with bristles, with the terminal joint exceedingly minute and lamelliform. 



