10 THE VOYAGE OF H.M.S. CHALLENGED. 



The specimen is a male and measures 16 mm. in length. 



The body is everywhere of the same approximate breadth, and is therefore somewhat 

 oblong in shape. 



The head is of a smaller diameter than the thoracic segments, it is prolonged between 

 the antennas into a rostrum, the peculiar shape of which can be understood by an 

 inspection of fig. 1 ; on either side of this the anterior margin of the head is somewhat 

 curved and projects as a short process to the outside of the insertion of the antennules, 

 the lateral regions of the head are prolonged into a rhomboidal area, the apex of which 

 is directed forwards. 



All the segments of the thorax are pretty much of equal length and breadth ; the 

 first three segments are slightly crescentic in form, the convex margin being directed 

 forwards ; the fourth segment is as nearly as possible straight ; the succeeding segments 

 are concave backwards, the depth of the concavity increasing progressively. 



The dorsal surface of these segments is perfectly smooth and rather flattened. The 

 lateral margin of the first thoracic segment is prolonged into a curved and somewhat 

 forwardly directed triangular spiny process, the base of which occupies as it were the 

 whole of the lateral margin of the segment ; in the second segment there is a very 

 narrow antero-lateral spiny process ; the two following segments are similar save that 

 the antero-lateral process is somewhat stouter, and there is also a short postero-lateral 

 process between which the margin of the segment is perfectly straight. In the fifth 

 segment the antero-lateral process becomes much wider, occupying nearly the whole of 

 the lateral margin; in the two remaining segments the lateral process is broad and as 

 wide as the segment itself. The epimera absent in the first segment are elsewhere short ; 

 in the second, third, and fourth segments the epimera are bilobed processes projecting 

 outwards from the middle of the lateral margin of the segments ; in the fifth, sixth, and 

 seventh segments the free margin of the epimera is rounded, and these structures come to 

 lie at the postero-lateral margin of their segment, becoming also gradually reduced in 

 size in the successive segments. 



The caudal shield is about as long as the three last segments of the thorax ; it is 

 subquadrangular in outline ; its margins, as well as those of the thoracic segments 

 generally, are beset here and there with fine long unbranched hairs as are also the 

 margins of the thoracic segments. 



The eyes have the peculiar form that is characteristic of the genus ; they occupy a 

 narrow oblong area which is set nearly transversely but also somewhat obliquely to the 

 longitudinal axis of the body. 



The antennules (fig. 2) are made up of four basal joints and a long flagellum, longer 

 than the peduncle ; the proximal joint of the antennules is mucli thicker than the two 

 succeeding ones ; of these two the more distal is the longer, the fourth is very short 

 indeed ; the proximal portion of the flagellum is not jointed. 



