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



6. Lexicon assimilis, n. sp. (PI. IV.). 



Specific Characters. — Form of body moderately slender. Carapace with the antero- 

 lateral corners triangularly produced, dorsal crest densely serrate, three of the denticles 

 placed near the posterior margin at some distance from the others ; pseudorostral 

 projection triangular, scarcely occupying one-fourth of the length of the carapace. 

 Inner flagellum of antennulae very small and knob-like. First pair of legs slender, with 

 penultimate and antepenultimate joints subequal ; second pair with terminal joint narrow 

 and linear. Uropoda with inner branch shorter than outer, last joint scarcely half as 

 long as first, both joints strongly spinulose on the inner edge. Length, 9 mm. 



Remarks. — This form is very nearly allied to the northern species, Lexicon nasicus, 

 Kroyer, from which it may, however, be distinguished by the somewhat different form of 

 the pseudorostral projection, which is comparatively shorter and simply triangular, not 

 as in that form obliquely truncate at the tip. 



Descrijition. — The form of the body (PI. IV. figs. 1, 2), as in most of the species, is 

 rather slender, though somewhat less so than in Lexicon nasicus, and slightly compressed, 

 especially in the anterior part, with no sharply-marked definition between the anterior 

 and posterior divisions. 



The carapace, occupying about half the length of the anterior division, is rather deep 

 and distinctly compressed, with a well-marked crest running along the dorsal side. This 

 crest is somewhat arcuate in the anterior part and densely denticulate, the denticles 

 having the form of regular serratures, from eighteen to twenty in number, the three 

 posterior of which are removed from the rest and placed at a short distance from the 

 posterior margin of the carapace. Between each pair of serratures a small hair is 

 affixed. The pseudorostral projection scarcely occupies one-fourth of the length of 

 the carapace, and is triangularly pointed (see fig. 3), with the upper edge quite smooth 

 and horizontal, the lower edges finely denticulate in the outer part and provided with 

 slender bristles. The fissure limiting the frontal lobe is distinctly marked, and just 

 above it on each side there are three small denticles. The end of the frontal lobe does 

 not exhibit any distinct ocular prominence, and the eye is wholly wanting, as in the other 

 species of the genus. The antero-lateral corners of .the carapace are distinctly projecting 

 and triangular in form ; between them and the pseudorostral projection the edges of the 

 carapace are evenly incurved and finely denticulate. The inferior edges of the carapace 

 are strongly serrate in the anterior part, and posteriorly curve slightly upwards to the 

 rounded postero-lateral corners. 



Behind the carapace five distinctly defined segments belonging to the trunk are 

 exposed, all of them having broad laminar epimera slightly projecting laterally. Of these 

 segments the first is very narrow, the others about equal in length, but successively 

 diminishing in height, so that the last segment is not higher than the caudal segments, 



