NO. 6.] ACCOUNT OF THE SPECIES. 93 



also mentioned by Dr. Giesbrecht as occurring in the species examined by him, 

 was at first overlooked, owing to its being partly concealed by the outer ramus, 

 and it is not indicated in the figure here given. The outer ramus is fully twice 

 as long as the inner, and much broader. The natatory seta of the 1st joint is 

 wanting, and in the 2nd joint it is replaced, as in Heterochceta, by a strong 

 denticulated spine, which in the present form is somewhat deflexed and a 

 little shorter than the terminal joint. The latter is considerably larger than 

 the other 2 joints combined, and is of oblong oval form, carrying 4 short nata- 

 tory setae inside, 2 extremely small spines outside, and at the tip another very 

 short and blunt spine. The inner ramus is of the same structure as in Hetero- 

 chceta, except that its terminal joint is comparatively larger, being fully as 

 long as the other 2 combined. 



The adult male (PI. XXVI, fig. 3) resembles the female in its general 

 habitus, but is easily recognizable by the structure of the left anterior 

 antenna, the last pair of legs, and the tail. The latter is very slender, 

 cylindric, and composed of 5 well-defined segments, which do not greatly 

 differ in size. The caudal rami with their setae are exactly as in the 

 female. 



The left anterior antenna (see fig. 3) is somewhat shorter than the right, 

 scarcely reaching, when reflexed, beyond the caudal rami. It is distinctly 

 geniculate at about the distal third part of its length, the 6 or 7 articulations 

 preceding the geniculation being somewhat dilated, and containing the usual 

 muscular band acting upon the terminal part. The latter (see fig. 4) is com- 

 posed of 4 articulations, the 1st of which is the largest. The 2nd articulation 

 is about the length of the last 2 combined, and is produced at the end 

 anteriorly to a long styliform process, extending almost to the end of the last 

 articulation. 



The posterior antennae, oral parts, and the 4 anterior pairs of legs do 

 not exhibit any perceptible difference in their structure from those appendages 

 in the female. 



The last pair of legs (PI. XXVII, fig. 10), however, are somewhat 

 different, especially as regards the outer ramus, which is more robust, and 

 has no spine inside the 2nd joint, nor yet natatory setae. This ramus 

 moreover, is slightly dissimilar on the two legs, as shown by the figure here 

 given ; but the dissimilarity is far from being so conspicuous as in Heterochceta. 



