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



form, articulating with the meros at its extremity, and bending at a right angle with it. 

 The meros is long and broad, flat on the inner and rounded on the outer side ; lower 

 margin straight, and armed with fine teeth and numerous long hairs ; upper margin 

 convex, and fringed with coarse strong teeth ; articulates with the ischium by an oblique 

 joint with lateral movement. The ischium is triangular, long and denticulated on the 

 lower side, except near the distal extremity, where it is fringed with long hairs ; the 

 outer margin is represented only by a point at which the articulation of this joint meets 

 the meros on one side and the coxa on the other, the basis being short and fused with 

 the ischium. The coxa is stout and robust, and supports a short, stiff mastigobranchia, 

 similar to, but a little longer than, that on the first pair of pereiopoda, and a well- 

 developed podobranchial plume, at the base of which stand two fasciculi of branchial hairs. 

 The second, third, and fourth pairs of pereiopoda resemble each other. The dactylos 

 is curved in a reverse direction from the common plan ; it is straight for some distance, 

 and the apex terminates in an outward and forward curve. The posterior margin is 

 fringed with hairs; the anterior surface has two lines of elevation or crests, the inner or the 

 one nearest the body is thickly fringed with hair, the outer is armed with a row of strong 

 teeth, which terminates in the apex or unguis. This joint is not capable of being bent 

 at more than right angles with the propodos : the propodos is subcylindrical, longer 

 than broad, the upper margin is wide and armed with tufts of hair ; the carpos is long, 

 nearly as long again as the propodos, gradually narrowing from the distal to the nearer 

 or meral articulation ; meros long, laterally compressed, the anterior and posterior margins 

 parallel and serrato-denticulated ; ischium and basis fused together, about half the length 

 of the meros, denticulated on the posterior, and mostly on the anterior margin ; coxa 

 large, quadrate. In the female those of the third pair approach each other, and are 

 perforate near the interno-posterior angle for the vulva, near which the coxa articulates 

 with the ventral surface of the pereion, whereas in the fourth pair the articulation is near 

 the centre of the posterior margin of the coxa, instead of at the inner angle ; the two 

 limbs are distant from each other, being attached to wider ventral plates. In both these 

 pairs of pereiopoda the coxa supports a short mastigobranchial appendage, of which the 

 posterior is the longer. Both are fringed with short hairs along the lower margin, and 

 tipped with long ones at the extremity. 



The fifth pair of pereiopoda articulates with a somite that is not fused with the rest 

 of the pereion. It much resembles that of the preceding pair, but is more cylindrical 

 generally, especially as regards the meros. The ischium is shorter, the propodos longer, 

 and the dactylos not excentrically curved. The coxa is large, deeper than broad, and 

 approximates very nearly to that of the opposite side. 



The first pair of pleopoda in the female is a three-jointed styliform appendage, short 

 and closely impacted in the ventral groove of the posterior somite of the pereion. 



The following four pairs of pleopoda are long, slender biramose, on a long basisal 



