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



The ophthalmopod is about half the length of the carapace, or a little longer than 

 the rostrum, narrow at the base, and gradually widening until it readies the ophthalmus, 

 which is slightly broader than the stalk at its distal extremity. 



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

 ophthalmopod, broad at the base, where it is expanded to contain the otocyst, and armed 

 with a small tooth or point, from whence it is narrow and cylindrical to the extremity ; 

 the second joint is about one-third the length of the first and slightly longer than the 

 third, which supports a long and slender flagellum that makes the antennae equal to two- 

 thirds the length of the animal. 



The second pair is longer than the first, being about equal to the length of the 

 animal, and carries a scaphocerite that is as long as the peduncle of the first pair, armed 

 near the distal extremity with a strung tooth, and having the inner margin fringed with 

 long bail's. 



The first and second pairs of gnathopoda are so far developed as to assume the 

 character in the adult. 



The first pair of pereiopoda also resembles that of the adult animal, but has not yet 

 prehensile power developed, and at the base, on the anterior margin, stands a small 

 tubercle that is probably of specific value ; a similar process is placed in the same 

 position on the second pair of pereiopoda, but is absent from the third. The second 

 and third pairs differ from those in the adult in not terminating in a small chela ; the 

 small terminal dactylos is not yet developed, and in its place there are two long terminal 

 hairs. The fourth and fifth pairs are not yet visible, even as buds. 



The pleopoda are long, slender, and well advanced in development ; the first pair is 

 single-branched and the following pairs are biramose. The terminal pair is long and 

 narrow, fringed with hairs on both sides, but not armed with a tooth on the external 

 margin of the outer plate. 



Length, 7 mm. (0'3 in.). 



Habitat. — The Western Pacific Ocean. 



A very closely allied specimen (PI. LXVII. fig. 5) was taken in the North Pacific, but 

 it differs in having the rostrum shorter, it being scarcely more than one-third the length 

 of the ophthalmopod (5a), and in having a small tooth on the outer margin of the outer 

 plate of the rhipidura (5v); the second and third pairs of pereiopoda exhibit an incipient 

 chela (5/). It is probably a later moult, as the animal has arrived at the Sergestes stage. 



A third specimen was taken, also in the Western Pacific (PL LXVII. fig. 6), which 

 differs from the two preceding in not having the rostrum armed with a small tooth on 

 the dorsal surface, but a small elevation or protuberance occupies its place. There is also 

 another variation. In the specimen we have described (fig. 4) there is a- small tooth 

 projecting from the outer angle of the orbit. This tooth is still more prominent in the 



