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



The pleopoda are slender but not long, increasing in diameter posteriorly. The sixth 

 pair has the outer branch long, with the external margin straight, unarmed and smooth 

 from base to apex, and the inner margin thickly fringed with long ciliated hairs ; the 

 internal ramus is one-third shorter than the outer and furnished with ciliated hairs. 



In our specimen the second pair of gnathopoda has a peculiarity that is found in a 

 few other species, in having the coxa largely increased in diameter. The value of this 

 feature I have not been able to determine, but I think it is a character special to young 

 male specimens previous to the development of more distinctly sexual characters. 



This species closely approaches the two following. 



At the surface of the China Sea a specimen about 7 mm. in length was taken, that 

 corresponds with this species in all essential details, except that there is a little tooth 

 only on the fifth and sixth somites of the pleon, the fourth somite being smooth. This 

 variety differs from Sergestes ancylops, Kroyer, in having no tooth on the outer plate of 

 tlie rhipidura. 



Sergestes ovatoculus, n. sp. (PI. LXXIV. fig. 2). 



Rostrum short, slightly elevated above the line of the dorsal surface. Carapace more 

 than one-third the length of the animal. Pleon having the anterior five somites subequal 

 in length, the dorsal surface of the anterior four smooth, the fifth elevated into a strong 

 prominence in front of the posterior margin, the apex of which is crowned with a small 

 posteriorly projecting tooth. The sixth somite is equal to the combined lengths of the 

 two preceding ; it projects posteriorly in the dorsal median line to a blunt point, and 

 has the lower margin fringed with ciliated hairs. 



The telson is narrow, tapering, has the lateral margins fringed with numerous,* long, 

 ciliated hairs, and terminates in two small teeth. 



The ophthalmopoda are about half the length of the carapace, or a little longer than 

 the first joint of the peduncle of the first pair of antenna?. The ophthalmus is ovate, 

 much broader than the stalk and abruptly enlarged to a fungiform shape. 



The first pair of antennae has the first joint of the peduncle as long as the stalk of 

 the ophthalmopod, the second joint about half the length of the first, and the third 

 nearly twice as long as the second ; the longer fiagellum is lost in our specimen. 



The second pair of antenna? has the last joint of the peduncle terminating subequally 

 with the first joint of the first pair ; the fiagellum is lost ; the scaphocerite is narrow and 

 nearly twice as long as the ophthalmopod, and is armed with a tooth near the distal 

 extremity. 



The first pair of gnathopoda is the only set of appendages of the pereion preserved, 

 and offers no very distinguishing specific character. 



The pleopoda are tolerably long, robust, and gradually shorten posteriorly. 



