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



The first pair of antennae stands on a movable somite and has the first joint 

 dorsally excavated to receive the ophthalmopod ; it carries a long and pointed stylocerite 

 on the outer margin, and the rudiment of a prosartema, in the form of a tubercle tufted 

 with long hairs, on the inner side ; the third joint terminates in two unequal flagella 

 situated remotely from each other, the upper one, arising from the base, is half the length 

 of the peduncle, whereas the lower, which is more slender, is probably as long as the 

 animal, or longer. 



The second pair of antennae carries a broad scaphocerite, as long as the peduncle of 

 the first pair, strengthened by a pointed tooth on the outer margin, and by one on the 

 second joint of the peduncle. 



The mandible has a lunate psalisiform margin and a broad molar tubercle, and carries 

 a two-jointed synaphipod, the terminal joint of which is laterally excavate. 



The third pair of siagnopoda is four-branched ; the inner branch is broad, foliaceous 

 and hirsute, the second is three-jointed; the next is foliaceous, narrow, and terminates 

 in a slender point, while the outer is a bifid membranous plate. 



The branchiae are arranged as in the following table : — 



Pleurobranchise, 

 Artbrobranchiae, 

 Podobranchise, 

 Mastigobranchia.'. 



The rostrum in the single Challenger specimen is broken off, but I am inclined to 

 believe that it corresponds in form to that in Aristeus. The outer antennal tooth is larger 

 than in that genus, and there is also a hepatic tooth, which the species of Aristeus do 

 not possess. 



The ophthalmopod corresponds in form more to that in the genus Benthesicymus 

 than in Aristeus, whereas the antenna? correspond rather to those of the latter 

 genus. 



The mandibles differ in having a larger molar tubercle, and in having the incisive 

 margin simply curved, with a sharp tooth at either extremity, while in Aristeus there is 

 a strong tooth in the centre also. 



The first pair of oral appendages has the outer branch thin, foliaceous, and produced 

 to a slender point, and in this it corresponds with Benthesicymus and differs from 

 Aristeus. 



The branchiae differ from both genera in the number of the plumes ; in ultimate 

 structure they correspond with those in Hemipenieus tomentosus more than with those 

 in either Aristeus armatus or Benthesicymus crenatus, the types of their respective 

 genera. 



