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



The exposed part of the trunk is composed of five well-defined segments, the three 

 anterior of which are somewhat gibbous dorsally and provided above with a short 

 transverse row of small denticles. The epimera of all the segments are distinctly 

 marked and laterally extended ; those of the three anterior segments produced anteriorly 

 as an acute angle. Of the segments, the second is the largest, the last being very small, 

 scarcely broader than the caudal segments. 



The tail is extremely slender and elongate, almost twice as long as the anterior 

 division of the l)ody. Its segments are cyliudiical, with the posterior margin slightly 

 emaro-inated above and below. They taper somewhat posteriorly and increase successively 

 in length to the penultimate, which is very elongate. The last segment is much shorter 

 than the others, somewhat depressed and expanded at the end. 



The integuments are not very strong, though somewhat more indurated than in the 

 other forms belonging to this family, and they exhibit a slight squamous structure. 



The colour— to judge from a fresh specimen mounted in Canada balsam — is uniformly 

 yellowish, without any pigmentary spots or ramifications. 



The antennulfe (PI. II. fig. 9) are remarkable for their unusual size, being almost as 



long as the carapace, and also for the great development of the flagella. The peduncle 



is rather elongate, and as usual, composed of three distinctly defined joints. The basal 



joint is about as long as the two others taken together, slightly curved, and provided at 



the end with several strong, partly ciliated bristles, and a few small denticles. The two 



succeeding joints are scarcely narrower than the basal and densely setose, especially 



towards the inner edge ; some of the setse are ciliated, some simple and very slender. 



The second joint, like the basal, is finely denticulate at the end, and somewhat larger 



than the third. Of the flagella, the outer one is almost as long as the peduncle, and 



composed of no less than six distinctly defined joints— a quite unusual number— each 



provided at the end with slender simple bristles. Of the joints, the first and penultimate 



are the longest, whereas the last joint is very small and might Ije easily overlooked. 



Besides the bristles, this flagellum bears at the tip two ribbon-like, densely articulated, 



sensory appendages, one of which originates from the end of the penultimate joint, the 



other from the last joint. The inner flagellum, which in the Cumacea generally presents 



a more or less rudimentary state, is rather fully developed, only slightly shorter than the 



outer, and composed of three slender joints of about equal size, and beset with bristles. 



In the young male the antennulse (see PI. III. fig. 14) do not differ materially from those in 



the female, except by the peduncle being slightly thickened, and by the first joint of the 



outer flagellum being somewhat expanded at the base ; in all probability in the adult male 



this joint bears a bunch of sensory appendages, as in the males of several other Cumacea. 



The antenna} in the female (PI. II. fig. 10; PL III. fig. 1, a') are less rudimentary 



than in most other Cumacea, forming a slender stem composed of five distinctly defined 



joints. Of these the four first represent the peduncle, and the last the flagellum. 



