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



The second pair of antennae, which is broken at the extremity of the peduncle, has 

 the basal joint armed on the outer and lower angle with a strong tooth, and carries a 

 scaphocerite that is as long as the peduncle of the first pair of antennae ; it is narrow 

 and has the margins parallel, the outer being armed with a long tooth near the distal 

 extremity, and the inner fringed with long, slender, and distantly planted hairs. 



The metastoma has no tooth at the anterior margin, but is produced to a blunt 

 point. 



The mandibles carry a strong two-jointed synaphipod. 



The first pair of gnathopoda terminates in a long, ovate, spatuliform joint. 



The second pair of gnathopoda is not remarkable for its length, and the terminal 

 joint is only in an incipient stage of development. 



The first pair of pereiopoda is wanting, being apparently broken off at the coxal 

 joint. The second and third pairs are moderately long and terminate in incipient chela?. 

 The last two pairs are wanting and appear to be in an early stage of gemmation, and 

 the two somites which support them are not appreciably distinct, and support on each side 

 two small branchial plumes in an incipient stage of development. 



The first pair of pleopoda is long, slender, and single-branched ; the four succeeding 

 pairs resemble the first, but carry a small secondary branch attached to the anterior 

 angle of the distal extremity of the basal joint, which is more robust in the anterior and 

 foliaceous in the following pairs, each successively increasing in length posteriorly. 



The posterior or terminal pair is very long, being twice the length of the telson or 

 quite equal to two-thirds of the length of the pleon. The plates are narrow and slightly 

 curved ; the outer is armed with a strong tooth near the middle of the margin, and is 

 fringed with cilia on the inner and distal margins. 



Length, 3 '5 mm. (0 - 14 in.). 



Habitat. — North Pacific Ocean. 



Observations. — This species bears so close a resemblance to Sergestes brachyorrlws, 

 Kroyer, that I was at first induced to believe it might be a younger form of that species, 

 an opinion that received support from the form of the rhipidura and scaphocerite. 

 It differs, however, from that species in the length of the telson, the shortness of 

 which in Kroyer's species having probably suggested the specific name. The outer plates 

 of the rhipidura are furnished with a strong tooth on the outer margin, and the narrow 

 form of this appendage and of the scaphocerite is strong evidence of incomplete 

 development. The absence of the fourth and fifth pairs of pereiopoda, or at least their 

 presence only in a stage of incipient budding, is suggestive of this animal being the 

 young of the genus Acetes — a genus that I have not had the opportunity of studying 

 with care, as there does not appear to be a specimen of it in the extensive collection of 

 the Challenger. But since Professor Brooks is inclined to believe that up to a certain 



