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



The first pair of antennae (fig. lb) has the peduncle about two-thirds the length of the 

 carapace, and its three joints subequal. The longer flagellum is broken off in all our 

 specimens, but Kroyer states that it is about two-thirds the length of the animal, and 

 is furnished with a small, rudimentary, secondary branch. 



The second pair of antennas is broken off in our specimen at the extremity of the 

 peduncle, and Kroyer gives it as deficient also ; it carries a long, narrow scaphocerite, 

 about as long as the peduncle of the first pair of antennas, and has the margins nearly 

 parallel, the inner being fringed with ciliated hairs and the outer smooth and armed at , 

 the distal extremity with a small tooth. 



The oral appendages were not specially examined. 



The first pair of gnathopoda does not differ from the typical form. 



The second pair is long and slender, being about three-fourtbs the length of the body 

 of the animal ; all the joints except the coxa are subecmally long and slender, the two 

 distal joints being fringed with long hairs. 



The first pair of pereiopoda is short, being scarcely more than half the length of the 

 second pair of gnathopoda, and is furnished with a brush of short spine-like hairs on 

 each of the adjacent surfaces of the carpo-propodal or ultimate articulation, which 

 gives the appendage a feeble prehensile power. The dactylos of this pair of appendages 

 is absent. The second and third pairs of pereiopoda are slender, about as long as the 

 first pair of gnathopoda, fringed with tolerably long bail's, and terminate in small chelae. 

 The fourth and fifth pairs are more rudimentary in the Challenger specimens than in 

 Kroyer's figure, the animal probably being younger. 



The pleopoda in the female specimen are moderately long and slender, except the 

 sixth pair, which forms the outer plates of the rhipidura ; the outer branch is rather more 

 than twice the length of the telson, and is armed with a small tooth on the outer side 

 about one-third from the base ; from the tooth the margins gradually taper to the apex, 

 and are fringed with long ciliated hairs. 



Observations. — The dorsal surface of the carapace appears to be broader than is 

 generally the case in this genus, but our specimen, from its small size, is probably not a 

 full-grown animal. A specimen that appears to be a younger or Mastigopus form of 

 this species was taken about 60° of west longitude of Station 256, but approximately 

 in the same latitude. It is about 4 mm. in length, and differs chiefly in those features 

 that are characteristic of a younger animal. The scaphocerite is longer and has the 

 margins more nearly parallel than in Kroyer's figure, though not more so than in the 

 animal represented in our figure. The telson and the plates of the rhipidura are 

 narrower than in Kroyer's figure or in our type specimen. The dorsal surface of the 

 pleon is armed with only three teeth, one on each of the three posterior somites, 

 whereas Sergestes armatus is armed with four, one on the second, third, fourth, and 

 fifth respectively, but none on the sixth. This difference in the dorsal armature is the 



