REPORT ON THE CRUSTACEA MACRURA. 399 



more than one-sixth the length of the preceding, and feeble in character. The fifth 

 pair is about half the length of the fourth, and almost rudimentary. 



The pleopoda are long and slender, but gradually shorten in length posteriorly ; the 

 first pair is single-jointed, the others biramose. 



The sixth pair is long, and forms the lateral plates of the tail-fan, of which the outer 

 plate equals the sixth somite in length, and is armed with a tooth on the outer margin, 

 one-fourth distant from the distal extremity ; the outer margin beyond is fringed with 

 hairs, as is also the inner margin and both margins of the inner plate. 



Length, 10 mm. (0'4 in.). 



Habitat. — The Pacific Ocean (December 16, 1875), between Valparaiso and Juan 

 Fernandez ; in the towing net at a depth of 200 fathoms. 



Sergestes diapontius, Spence Bate (PL LXXII. fig. 3). 

 Sergestes diapontvus, Sp. E., loc. tit., p. 194. 



Eostrum short, prominent, sharp-pointed and directed oblicpiely upwards, and elevated 

 a little above the dorsal surface of the carapace, which is about one-fourth the length 

 of the animal, including the telson. 



Pleon with the three anterior somites subequal in length and dorsally smooth. The 

 next two are about the same length, and dorsally armed with a tooth a little within the 

 posterior margin. The sixth somite is shorter than the two preceding combined, dorsally 

 smooth, and less deep than the fifth. Telson nearly as long as the rhipidura. Ophthal- 

 mopoda less than half the length of the carapace ; ophthalmus not broader than the 

 distal extremity of the stalk, which gradually tapers to the base. 



First pair of antenna? with the first joint of the peduncle short, about one-third the 

 length of the ophthalmopod, the second twice as long as the first, and reaching cpiite 

 to the extremity of the ophthalmopod, and the third nearly as long as the second, 

 but narrower, and supporting a long, slender flagellum that reaches to about one-half the 

 length of the animal. The base of this flagellum is slightly enlarged, and carries a brush 

 of membranous cilia, and a small rudimentary secondary flagellum. 



The second pair of antenna? has the terminal joint of the peduncle broad, and longer 

 than the first joint of the first pair, and reaching to nearly half the length of the second 

 joint ; scaphocerite nearly as long as the peduncle of the first pair, or reaching at 

 least to half the distance of the third joint ; flagellum long and slender, tapering to 

 a fine thread, and nearly once and a half as long as the animal. 



First pair of gnathopoda not specifically peculiar. 



Second pair long and robust, being nearly as long as the animal ; coxa, basis, 

 ischium, and msros long and subcyliudrical, carpos long and slender, rather longer 

 than the meros, propodos shorter than the carpos, and divided into three or four articuli 



