338 PERCY SLA DEN TRUST EXPEDITION 



Its gill will be mentioned later. A swelling which is sometimes present at the base 

 of the coxopodite may represent the precoxal endite. 



The main axis of the third maxilliped (^ in figs.) consists, in Urocaridella (Plate 53, 

 fig. 2i), of five joints, the ischiopodite being fused with the meropodite, and the propodite 

 with the dactylopodite. Curiously enough, this arrangement is found also in Concho- 

 dytes (Plate 57, fig. 26 i) at the other end of the pontoniine series. In all other genera 

 the basipodite is fused with the ischiomeropodite, though the junction is still marked 

 by a notch. The coxopodite bears on the outside a small, rounded epipodite, and 

 often also on the inside a knob with bristles which is perhaps to be regarded as an 

 endite. The exopodite is obscurely annulate and at its end there are usually a few 

 longer segments, which are sometimes true joints but in other cases appear to be 

 marked merely by a change in the width of the organ and the attachment of bristles. 



The long joint of the endopodite (ischiomeropodite) is in Urocaridella (Plate 53, fig. 2*") 

 and Urocaris (Plate 53, fig. 3 i) straight, with the out6r side somewhat swollen at the 

 base. In the other genera it is almost always more or less curved, with the concave side 

 towards the middle line of the body. It is always ribbon-like, and shows throughout the 

 subfamily a tendency to widen. It is narrow in Urocaridella, Urocaris, Ancyclocaris, 

 PalcBmonella, Periclimenes, Periclimenceus , and Pontoniopsis, though in some species of 

 Periclimenes (Plate 54, fig. 8 i) and in Periclimenceus (Plate 55, figs. 19 and 20 i) it is a little 

 increased in width. In Ilarpiliopsis (Plate 55, fig. 21 and Plate 56, fig. 22 i), Coralliocaris 

 (Plate 56, figs. 23 and 24 ^), and Anchistus it is wide or narrow according to species, reaching 

 in some Anchistus the greatest width it attains in the subfamily. In Harpilius it is wide, 

 but narrows towards the distal end. In Pontonia and Conchodytes (Plate 57, fig. 26 ^) it is 

 broad. The last two joints are always a little narrower than the ischiomeropodite, but are 

 of approximately the same width as it in the species in which it is narrow and in Corallio- 

 caris. In Harpilius, in some species of Anchistus, and in Harpiliopsis beaupresi, they 

 remain narrow though the ischiomeropodite is expanded. In Pontonia and Conchodytes 

 they are wide, though the widening is not equally pronounced in all species. They 

 have always a flat ventral surface but are sometimes, as in Coralliocaris, stoutly 

 built. The curving of the ischiomeropodites brings the last two joints of each third 

 maxilliped near to those of its fellow, so that, while the ischiomeropodites lie at the 

 sides of the mouth, with a wide gap between them, in which the second maxillipeds 

 are exposed, the distal parts of the limb lie side by side in front of the mouth region. 

 A further complexity in the arrangement of the parts of the limb is brought about by 

 the fact that the ischiomeropodites are twisted, so that the flat surface of the appendage, 

 which in its distal pa.rt is in a horizontal plane, is in the proximal part in a plane 

 between the horizontal and the vertical. This arrangement has the efiect of forming 

 a kind of basket below the mouth region, walled in at the sides by the ischiomeropodites, 

 which are of course more efiicient in that respect the wider they are, and by the long 

 bristles which project downwards and inwards from the median edges of these joints. 

 In front, the distal part of the limb, with its bristles, affords a surface, horizontally 

 placed below the antennal region while the appendages are outstretched, which by 

 bending can be brought ventrally under the mouth area to complete its enclosure. 



