EEPOET ON THE CUMACEA. 51 



branchial regions, and the posterior part of the carapace considerably narrower than in 

 the female. As to the armature of the carapace, it differs materially from that in the 

 female by the almost complete want of the spinules, of which only a slight trace can be 

 obsei'ved in the most anterior part. Moreover, on the sides of the carapace, below the 

 middle, a distinctly marked keel runs from the postero-lateral corners forwards, 

 limiting the greatly swollen branchial regions below. This keel, found in all adult 

 males of the present genus, is in some species strongly denticulate throughout, and thus 

 gives the caraj^ace a still more anomalous appearance. 



The exposed part of the trunk is considerably narrower than in the female, and less 

 vaulted, whereas the epimeral plates are more distinctly defined and setose at the edges ; 

 those of the last segment especially exhibit a rather peculiar form, each being produced 

 posteriorly to an acute point, and bearing at the outer edge four very strong and 

 densely plumose setaj. 



Of the caudal segments, the two anterior are somewhat thicker than the others, and 

 have, moreover, a serrate crest running along the ventral surface, the crest being also 

 continued along the last segment of the trunk. These segments are otherwise quite 

 smooth, without any dorsal denticles. 



The anteunulse (PI. VIII. fig. 1, a^ ; fig. 2) are comparatively stouter than in the 

 female, with the outer part of the peduncle less slender, and provided at the base of the 

 outer flagellum with a dense fascicle of delicate sensory filaments. The flagella are 

 nearly ecpxal in length, and each of them has one joint more than in the female, a short 

 articulation being marked off at their base. 



The antennae (fig. 1, a" ; fig. 3) are greatly developed, and fully as long as the whole 

 body. The peduncle is strongly geniculate, with the proximal part consisting of four 

 short and somewhat irregular joints, connected together by rather oblique articulations; 

 it bears at the base three strong ciliated bristles curving anteriorly, two of which issue 

 from the second joint, and the third from the first. The distal reflexed part of the 

 peduncle constitutes a single, very large and slightly compressed segment, gradually 

 tapering to the apex, and provided along the outer edge with numerous fascicles of short 

 sensory bristles. Within this segment several strong muscles are seen converging to 

 the tip; by the aid of these muscles the flagellum is moved. The latter is extremely 

 slender and composed of very elongate articulations, each provided at the outer edge 

 with numerous fascicles of small sensory bristles of the same kind as those on the distal 

 part of the peduncle (see fig. 4). 



The oral parts do not seem to differ materially from those in the female. 



The branchial apparatus, on the other hand, is much more fully developed 

 (see fig. 1); the great number and peculiar arrangement of the gill-lobules being 

 especially remarkable. The gill-lobules also difler considerably in form from 

 those in the female, being distinctly lamellar, instead of digitiform (fig. 7). They are 



