REPORT ON THE CRUSTACEA MACRURA. 417 



the external plate is armed with a small tooth, one-third distant from the extremity, and 

 beyond that is fringed with hairs. 



Length, G mm. (0'25 in.). 



Habitat. — South Pacific Ocean. 



Observations. — This specimen is evidently one of the group that connects Sergestes 

 with Leucifer. The great length of the cephalon, the distance between the oral 

 apparatus and the frontal margin of the carapace, and the reduction of the two posterior 

 pairs of pereiopoda to a rudimentary condition, demonstrate its tendency to depauperisa- 

 tion in the direction of that genus. 



Sergestes longispinus, n. sp. (PI. LXXVI. fig. 2). 



Rostrum long, slender, and sharp, dorsally armed with a small denticle a little in 

 advance of the frontal margin, and about one-third the length of the carapace, which is 

 about one-third the length of the animal. 



Picon with the five anterior somites subequal, and dorsally armed with a strong 

 tooth; the two anterior teeth are small and anteriorly directed; the two succeeding 

 long, perpendicular, and spine-like, and the fifth small and directed posteriorly ; the 

 sixth somite is equal to the united lengths of the three preceding, but not so deep 

 laterally, and is dorsally armed posteriorly with a tooth that is directed backwards in a 

 line with the dorsal surface, and one also at the postero-inferior angle. 



The telson is long and slender, being more than half the length of the outer branch 

 of the rhipidura. 



The ophthalmopoda are fungiform and about as long as the carapace ; the stalk is 

 long and slender, and the ophthalmus much broader than the stalk. 



The first pair of antennse has the three joints of the peduncle subequal ; the terminal 

 rlao-ellum is broken off short. 



The second pair of antennas has the last joint of the peduncle long and cylindrical, 

 and the scaphocerite is long, narrow, and with parallel margins, the outer being smooth 

 and armed near the extremity with a sharp, slender tooth, and the inner fringed with a 

 series of ciliated hairs. 



The first pair of gnathopoda is rather short, but not specifically peculiar. 



The second pair of gnathopoda is long, with the basal joints robust, and the distal 

 slender and furnished with fine hairs. 



The first pair of pereiopoda (fig. 2k) is short, about half the length of the second pair of 

 gnathopoda ; the basis is armed with a small denticle or obtuse point, and the under or 

 posterior margin bears a series of distantly placed hairs, as also does the meros ; the 

 terminal joints are furnished with closely placed hairs, and the ultimate is reduced to a 



(ZOOL. CHAT.L. EXP. — PART LII. — 1886.) Fff 53 



