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



anterior segments are nearly equal in size, whereas the two succeeding somewhat increase 

 in length. The last segment is a little shorter than the preceding, slightly expanded at 

 the end and somewhat depressed. All the segments are quite smooth, without any trace 

 of spines or denticles. 



The integuments, as in the other species of the genus, are rather strong and 

 calcareous, exhibiting under the microscope a finely reticulate structure. 



The colour of the body is uniformly whitish, without any pigmentary deposits. 



No trace of a distinctly developed eye can be detected, though a small rounded ocular 

 lobe is present at the end of the median lobe (frontal lobe) (see fig. 2). 



The antennulae (fig. 5, a^) are rather slender, projecting considerably beyond the tip 

 of the pseudorostral projection. They are composed of a triarticulate peduncle, and two 

 well-defined flagella. The first joint of the peduncle is very large, considerably louger 

 than the other two taken together, and also much broader. It is somewhat flattened 

 and finely ciliate along the inner edge ; its end is obliquely truncate, and bears at 

 the inner projecting corner a very strong and densely hairy seta pointing anteriorly, 

 and at the outer a much smaller unciliated bristle, somewhat curved outwards. Of the 

 two outer joints of the peduncle, the first is the shorter, and has at the end internally a 

 ciliated seta of moderate size. The flagella are very unequal in size, the inner one being 

 very small, scarcely half as long as the last joint of the peduncle. Nevertheless, this 

 flao-ellum is found to be composed of three well-defined articulations, the middle one of 

 which is the longest ; at the tip of the last joint three unequal bristles are afiixed. The 

 outer flao-ellum is about three times as long as the inner, and composed of four articulations, 

 the three first of which are nearly equal in size, whereas the last is very small, and might 

 easily be overlooked. Besides two or three simple bristles, this flagellum bears at the 

 tip two slender ribbon-like sensory appendages, each divided into a number of short 

 regular segments. 



The antennae (fig. 5, a') have the form of simple, slightly tapering stems, about half 

 as long as the antennular peduncle, and somewhat curved outwards and forwards. Each 

 stem is composed of four well-defined articulations, and bears five strong, anteriorly 

 curved, plumose setae, two of which arise from the first articulation ; of these setae the 

 one afiixed to the penultimate articulation is considerably shorter than the others. 



The anterior lip (fig. 5, L) constitutes a rounded lobe projecting immediately behind 

 the antennal segment. The free edge of this lobe is slightly emarginate in the middle 

 and finely ciliated. 



The posterior lip (fig. 7) is considerably larger, but quite membranous, and, as usual, 

 consists of two lateral lobes united at the base. The lobes are irregularly oval and 

 have the inner corner slightly incurved, but without any teeth, whereas a fine ciliation is 

 found along the whole inner edge and part of the outer. 



The mandibles (fig. G) are strongly developed and rather similar in structure to those 



