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



The relative length of the joints one to the other varies in the different species, and 

 often afibrds a good ^^oint of distinction. 



The first joint may be ecj^ual to, or longer, or shorter than the second. In form it is 

 cylindiical, and the base has a narrow neck. The outer side is clothed with strong hairs, 

 which spring, as in other parts of the leg, from flat circular tubercles. On the inner side 

 some of the hairs are arranged in a regular series, and the general pubescence is finer. 



The second joint has also a neck at base, above which it is cylindrical, and with 

 paibescence similar to that of the first joint. 



At about the middle of its length the joint is cleft longitudinally into two unequal 

 parts (PL III. fig. 13). The upper and outer part (which may be looked upon as the 

 joint itself, while the lower and inner part may be called a process) is twice or three 

 times the length of the other part, but is only about half as thick as the basal half of 

 the joint. On the outer side it is rounded, but on the side facing the process it is flat or 

 slightly channeled, and destitute of pubescence. The hairs on the outer side are rather 

 coarse and adpressed, but towards the apex a few stronger, less adpressed hairs are mixed 

 with the others, and in some species at least two or three long stout hairs, with curved 

 extremities arise some way before the apex, and reach to or beyond it. 



The process, or shorter part of the cleft joint, is parallel to the other part. It is 

 somewhat triangular in outline, with a blunt apex, the outer side rounded and clothed 

 with rather long semi-adpressed hairs; the inner face furrowed and destitute of pubescence. 

 The fissure between the two parts is wider on the under side of the joint than on the 

 upper. 



At the bottom of the cleft are inserted the two curved sharp pointed claws (PI. III. 

 fig. 14), which are about double the length of the shorter division or process of the joint. 

 Each claw is rather broad, somewhat angularly keeled on the posterior surface, and slightly 

 concave on the other. At the base it is suddenly dilated posteriorly, the dilatation being- 

 triangular in outline. In one species {■wuHerstorjffi) the claws are about '23 mm. long, 

 'in another (sericeiis), they are about '17 mm. From between and a little behind the 

 claws arises a thin ribbon-like process about as long, but only half as broad, as the claws, 

 curved backwards, equally wide and thin throughout, and truncate at the apex (PI. III. 

 figs. 13 and 14). The use of this process is unknown. 



TJie Middle Legs. 



The Acetabulum has been already described. 



Tlie Coxa is cylindrical, much broader than long ; the apex is truncate, and fringed 

 with rather long hairs, which curve inwards ; it is hollowed to receive the expanded base 

 of the trochanter. 



The Trochanter (PL III. fig. 15, tr.) is al)out three times as long as broad. Its base is a 

 somewhat flattened ball, which fits into the hollowed apex of the coxa. Above the 



