1600 THE .VOYAGE OF H.M.S. CHALLENGER. 



is in this Report considered to be the first of the flagellum. The expression " first and 

 second pairs of thoracic legs " refers to the gnathopods ; by " the sixth segment of the 

 abdomen " is meant the double -segment composed of the fifth and sixth segments of the 

 pleon coalesced. The character, " telson short, triangular," is rather vague, since those 

 epithets, however applicable to the type of the genus, do not convey the idea of a 

 telson about four times as long as its greatest breadth, which are its dimensions in the 

 Challenger species. 



Calamorhynchus rigidus, n. sp. (PI. CCVI.). 



There appears to be a very close similarity between this remarkable species and the 

 type of the genus, Calamorhynchus pellucidus, Streets. The description of the head 

 given by Dr. Streets is almost exactly applicable to the present species, " head long, nearly 

 one-third of the total length, its breadth twice that of the thorax [perteon] ; the portion 

 containing the eyes oblong, convex above and below when viewed in profile, elevated 

 above, in the median line, into a sharp ridge, which terminates at the apex of the rostrum ; 

 below the eyes form two long and rounded lobes separated by a broad, shallow groove ; 

 rostrum flattened, posteriorly broader than the eyes, commencing on either side of the 

 eyes in a broad, rounded wing-like expansion, and tapering forward to a long and acute 

 apex." The whole animal is sharply angled along the median dorsal line. The middle 

 segments of the perseon rather longer than those at the two extremities ; the whole 

 length of the perseon subequal to that of the first three segments of the pleon together ; 

 the third segment of the pleon has the postero-lateral angles very acutely produced, the 

 second segment has them produced in a less degree than the third, and the first than the 

 second; the fourth segment is much shorter than either of the three preceding, and little 

 more than a third of the length of the coalesced fifth and sixth segments. 



Upper Antennas slender, first joint of the peduncle much longer than the second, 

 which is not longer than broad ; the first joint of the flagellum is in the present 

 species twice as long as the first of the peduncle (not, as in the type-species, subequal 

 to it), somewhat curved, with filaments at seven or eight points along the convex 

 margin and a couple at the apex of the opposite margin ; the second joint very much 

 thinner than the preceding, shorter than the first joint of the peduncle, with apical 

 filaments ; the third joint about half the length and breadth of the second, with apical 

 setules. 



Lower Antennae wanting in the female. 



Upper Lip. — The upper margin not evenly convex but with a little lobe in the 

 centre. 



Mandibles. — The cutting edge very oblique, finely striate and denticulate, having a 

 narrow, slightly produced tooth at the upper corner; the secondary plate of the left 



