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



The dorsal surface of the several somites of the pleon is smooth, but in the fourth it 

 is produced to a point, which in the two succeeding ones is increased to a decided 

 tooth. 



The telson tapers to a very sharp point, and has the sides compressed and the dorsal 

 surface flattened and slightly grooved in the median line. 



The ventral surface of the pereion is narrow ; the oviducts on the third pair of pereio- 

 poda come into contact in the median line. An almost vertical process, covered with 

 short stiff hairs, lies between the coxse of the fourth pair, behind which there is a 

 circular depression bordered by a hirsute ridge between the coxse of the fifth pair ; the 

 deep depression between the posterior two pairs of pereiopoda is sometimes filled with a 

 grey mass of firm and leathery texture (vide, PI. XLIX. fig. 3 ?). 



Between the first pair of pleopoda is an elevated ridge, and a prominent point exists 

 in the median line between the second. 



The ophthalmi are round and considerably broader than the ophthalmopoda, which 

 carry a rudimentary tubercle on the inner side near the eye. 



The first pair of antennas possesses on the inner side the rudiment of a prosartema 

 covered with long hairs, and on the outer side a stylocerite, in connection with the side 

 of the joint, extending to nearly the extremity of the external angle, which terminates in 

 a sharp point just in advance of it. Between the stylocerite and the inner margin the 

 surface is depressed into a deep hollow, the margins of which are thickly fringed with 

 tolerably long hairs ; the second joint is nearly as long as the first, and the third is 

 shorter and carries the short, outer flagellum near the base, and the inner and longer at 

 the apex. 



The second pair of antennae (PI. L., c) carries a large scaphocerite, the outer side of 

 which is strengthened by a slender ridge that terminates in a small sharp tooth somewhat 

 distinct from the rounded, pointed apex. 



The anterior three pairs of pereiopoda slightly increase in length posteriorly, and the 

 dactyli are adorned with small fasciculi of hairs at very regular distances. 



The first pair of pleopoda is long, slender, and single-branched, and has a small 

 l'udimentary petasma attached to the basal joint. The succeeding pairs are biramose, the 

 anterior branch, which is small in the second pair, increases gradually in size posteriorly. 

 The sixth pair, which forms the outer plates of the tail-fan, has the rami long and 

 terminate in a flat, foliaceous, ovate plate, the outer margin of which is strengthened 

 by a rib in the middle that meets the outer margin and forms a tooth somewhat short of 

 the extremity. 



The specimen taken at the New Hebrides was rather longer than those from the 

 Philippines, and was glabrous rather than tomentose. The rostrum was also a little 

 longer, stretching beyond the denticulation. In all other respects it corresponded very 

 closely with the typical form. 



