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



incisive blade of the mandible is wider and larger, and the molar protuberance within 

 is much less conspicuous. 



The first pair of gnuthopoda is similarly formed to the same organ in that genus, 

 but the basecphysis terminates in a sharp point only, instead of a multiarticulate lash. 



The second pair of gnathopoda corresponds much with that of Paraxius, but 

 carries a shorter and less conspicuous basecphysis, which does not terminate in a multi- 

 articulate lash. 



The first pair of j)ereiopoda varies but little in its relative symmetrical proportion, 

 the organ on the right side being the larger in the male, but subequal in the 

 female ; in both sexes they are large and powerful members, and have the propodos 

 laterally compressed and deeper than the carpos. The pollex is half the length of 

 the propodos, and is armed with a long flat central cusp and a few small serrate teeth 

 between it and the apex, which is sharp and turned a little upwards. The corresponding- 

 edge of the dactylos has a rounded tubercle near the joint, from which the margin 

 continues in an unbroken wavy line to the sharp and downward curved apex. 



The second pair of pereiopoda is much smaller than the first. It is chelate, the 

 propodos is long, the margins are parallel, and the dactylos strikes the pollex obliquely. 

 The third and fourth pairs of pereiopoda are subequal, and scarcely less robust than 

 the second parr, they are simple in structure, and terminate each in a short, flat com- 

 pressed lanceolate dactylos. The fifth is a more slender and shorter pair of appendages, 

 but similarly constructed to the last, and supporting a small brush of hairs on the inner 

 side at the base of the styliform dactylos. 



The first pair of pleopoda is small, slender, and rudimentary in the female, and appears 

 to be wanting in the male. The four next pairs of pleopoda are biramose, consisting of 

 a peduncle formed of the basisal joint and two long lamelliform branches, fringed with 

 deeply inserted long cibated bail's. The inner branch carries, one-third from the base, a 

 single straight stylamblys, which is armed laterally with a row of obtuse pointed curved 

 denticles to which Sars has given the name of " cincinnuli." In the male these branches 

 are smaller and less important, and the inner, instead of carrying one, supports two 

 stylamblydes. 



The sixth or posterior pair of pleopoda, which helps to form the rhipidura or fan -like 

 tail, is lodged in an excavation at the external angle of the posterior margin of the sixth 

 somite. The peduncle is short, the branches are as long as the telson, and are broad, 

 foliaceous, and terminally fringed with cilia. The telson is as long again as the sixth 

 somite of the pleon, it is long and rather quadrate in its form, and the terminal margin 

 is fringed with short cilia. 



The arrangement of the branchiae shows the greatest development in connection with 

 the three anterior pairs of pereiopoda, the number as well as the size of the plumes 

 diminishing both anteriorly and posteriorly. 



