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



The pleopoda are biramose, but those of the first pair have the inner branch developed 

 into a large membranous petasma, of considerably tenuity, to the inner margin of which 

 is attached a short stylamblys fringed with cincinnuli on the inner side. All the other 

 pleopoda are subequally biramose, and carry a long and slender stylamblys tipped with 

 cincinnuli, except the posterior pair, which is not perfect enough for description. 



Hymenodora, G. 0. Sars. 



Hymenodora, G. O. Sars, Archiv Mathem. Nat. Christiania, vii. p. 345, 1877. 

 Memngodora, Sidney Smith, BulL Mus. Comp. Zool., vol. x. p. 73, 1882. 



Integument soft and membranous. Carapace dorsally elevated and anteriorly pro- 

 duced to an imperfectly formed rostrum that does not project beyond the distal extremity 

 of the first joint of the first pair of antennae, and is formed by the meeting of the frontal 

 margin on each side with the dorsal carina in the median line, which is generally 

 furnished with a few small spinules. 



Pleon laterally compressed and more or less carinated posteriorly. 



Ophthalmopoda short, the ophthalmus imperfectly developed, and carrying both an 

 ocellus and a tubercle. 



First pair of antennas having the peduncle short, robust, terminating in two short 

 and unequal flagella. 



Second pair supporting a foliaceous scaphocerite and a long slender flagellum. 



Mandible supporting a three-jointed synaphipod. 



Second pair of gnathopoda pediform and carrying a long basecphysis. 



First two pairs of pereiopoda slender, subequal, and chelate, and both supporting a 

 basecphysis. Posterior three pairs simple and terminating in a sharp-pointed dactylos, 

 of which the posterior is the shortest. 



Pleopoda biramose, the first pair in the males having the inner branch developed in 

 the form of a petasma, and the outer branch of the rhipidura being long, and the telson 

 tapering. 



The animal is soft, and the integument very thin ; the carapace is dorsally subcarinate 

 or compressed to an angle which increases anteriorly and projects above the metope to 

 a point that never extends beyond the first joint of the first pair of antennas ; the dorsal 

 crest is generally surmounted by a row of minute denticles. The frontal margin slopes 

 from the apex of the rostrum continuously to the orbit, which is clearly defined at the 

 outer canthus by being lobed rather than pointed. The first antemial tooth is absent or 

 rudimentary ; the second is not largely projecting but is supported by a continuous ridge 

 more or less distinct from the hepatic region. 



The pleon has the first somite rather shorter than the others and dorsally rounded, 

 as is also the second, but the third, fourth, and fifth are carinated in the median line, the 



