134 THE VOYAGE OF H.M.S. CHALLENGEE. 



arisino- from the inferior maroin behind the middle, or, more precisely, just above the 

 point of insertion of the penultimate pair of legs. Its anterior part has a distinct, though 

 not very prominent keel running along the middle, and juts out as a rather narrow and 

 somewhat flattened rostral projection, reaching about the middle of the basal joint of the 

 antennulas. 



The caudal segments arc perfectly smooth aliove, and very narrow, with exceedingly 

 small, rounded ejumera. The last segment is appreciably longer than any of the 

 preceding, and has a very small, simple preanal spine. 



The eyes (see figs. 5, 6) are not very large, and of a somewhat clavate form, with the 

 cornea very narrow, and occupying but a small part of each eye. 



The antennular peduncle (ibid.) is very slender and elongate, attaining almost the 

 length of the carapace. The flagella, on the other hand, are exceedingly short, scarcely 

 exceeding half the length of the peduncle. 



The antennal scale {see fig. 6) does not reach beyond the second joint of the antennular 

 peduncle, and is very narrow, linear, with the apex obtusely truncate, and the outer 

 corner but slightly projecting. 



The first pair of legs (see fig. 5) are comparatively shorter than in either of the two 

 preceding species, and do not nearly attain the length of the body, wdien fully extended. 

 The geniculate bend between the meral and carpal joints extends to about the tip of the 

 antennular peduncle. The propodal joint, as in Nematoscelis micro2)S, is slightly longer 

 than the carpal, and the terminal joint is very narrow, almost linear, and provided with 

 only four slender spines, one of which projects far beyond the rest. 



The succeeding pairs of legs are very small, and difficult to examine without dissection. 



The gills are apparently far less complex in structure than the corresponding parts in 

 the two preceding species, the gill-lobules being few in number and merely papillar in form. 



The caudal fan does not exhibit any essential difference from that in Nematoscelis 

 microps. 



Habitat. — A few specimens of this slender species have been collected at the surface 

 -of the sea, in five different localities : — 



The distribution of the species w^ould accordingly seem to range from the tropical 

 part of the Atlantic to the tract of ocean surrounding the Indian Archipelago. 



