163 



THE VOYAGE OF H.M.S. CHALLENGER. 



extremity; the outer margin is fringed with denticles that become more conspicuous towards 

 the dactyloid extremity of the propodos, where they exist in two rows; the dactylos 

 resembles the pollex reversed, the lateral or palmate margins approximating, and having 

 the extremities curved to overlap each other, and there" is no tooth on its inner margin. 

 The inner margins of the dactylos and pollex are throughout fringed with a narrow row 

 or series of upright plates of extreme tenuity, the sides of which overlap each other 

 and form a delicate cutting edge. 



The mastigobranchise attached to this pair of appendages (k) are short and of extreme 

 tenuity from the base. Each is slightly longer than the coxa is wide ; it widens 

 increasingly and terminates in an obtuse point covered with hairs that are subspinose. 

 The podobranchial plume (Id") attached is a small and feeble structure, shorter than the 

 mastigobranchia. One of the arthrobranchise is also rudimentary, consisting only of a 

 few small branchial processes. The other is moderately developed. 



The second pair of pereiopoda is very much shorter than the first, and has the several 

 joints comparatively robust and flattened on the surface nearest the body, against which 

 the ischium and meros lie arched beneath the lower margin of the carapace. The pollex 

 and dactylos impinge against each other throughout their length, except the apices, 

 which cross one another. The inner surfaces of the pollex and dactylos are fringed 

 with a row of thin plates somewhat similar to those in the first pair, except that each plate 

 is produced to a sharp point, which gives a serrate character to the structure. Most of the 

 joints are fringed with rows of long hairs. This pair carries a mastigobranchia that sup- 

 ports a podobranchial plume, above which are two arthrobranchia? and a pleurobranchia. 



The third (PL XX. to) and fourth pairs of pereiopoda are smaller than the second, which 

 they generally resemble, particularly in the form of their chelse, except that the curved 

 unguis at the extremities of the antagonising pollex and dactylos are longer, so that 

 the apices meet or cross one another. These two pairs support branchial arrange- 

 ments similar to the preceding. 



The fifth pair of pereiopoda is shorter than either of the others, and lies directed 

 posteriorly. It terminates in a small chela that is similar in both sexes, and does not 

 support any branchial lash or plume, except a moderately developed pleurobranchia 

 situated high up beneath the carapace. The general arrangement of the branchiae may 

 be tabulated as follows : — 



The first pair of pleopoda in the female is two-jointed, uni-branched, long, slender, 

 and flat, with parallel sides, the margins being sparsely ciliated with hairs, and the 



