330 PERCY SLADEN TRUST EXPEDITION 



the surface of various objects on the sea-floor, or shelter without quiescence upon the 

 bodies of echinoderms, where they have neither a stable foothold nor great protection, the 

 habit of body is very much that of the Leander of the British coast — slender, but without 

 the attenuation of Urocaris. Periclimenes (Plates 54, 55, figs. 10 — 16) shows considerable 

 variety in body form, and this is no doubt connected with differences in habitat and 

 activity. Periclimenceus (Plate 55, figs. 19, 20) is an aberrant group of Periclimenes 

 which has taken on an Alpheus-like habit of body, no doubt in accordance with some 

 special mode of life. ^ Pontoniupsis, commensal with a crinoid, is more modified in 

 respect of some of its organs than is Periclimenes, but in regard to habit of body 

 is in much the same condition. Ancyclocaris, living within the zone of protection of 

 a large sea-anemone, whose mouth it even enters at times, has a more stoutly built 

 body with, in the female, a huinp on the back of the thorax which suggests some 

 peculiarity in the ovary. Harpiliopsis. Harpilius, and Coralliocaris are adapted by 

 their heavy, depressed bodies to a sluggish life among the branches of coral stocks, 

 in that habitat which swarms with Trapezia and other small crabs, and is such a 

 rich collecting ground for the marine zoologist in the tropics. Stegopontonia is an 

 aberrant member of this group of genera, adapted for an existence spent among the 

 spines of a sea-urchin, and Coutierea, also related here, bears, with its spiny, keeled 

 abdomen, and long rostrum and supraorbital spines, the characteristic appearance of a 

 deep sea crustacean. Anchislus, Pontonia and Conchodytes, which live within the shells 

 and tests of bivalves and ascidians, have reached the highest degree of specialization 

 in the subfamily. Their swollen, clumsy bodies, though not more depressed than those 

 of Coralliocaris and Harpiliopsis, have in some cases almost lost the semblance of 

 prawns, and suggest degeneration as strongly as that of the crab Hapalocarcinus, 

 to which they bear no little resemblance. Typton, though heavily built, is compressed 

 and prawn-like, and is no doubt adapted by its shape to life in the canal system 

 of the sponges which it inhabits. In all these cases, the male, though his body tends 

 to undergo the same modifications as that of his mate, has a more normal appearance 

 than she, principally because his abdomen is less enlarged (Plate 57, fig. 29). 



Thoracic sterna are distinct and well formed in all genera of the subfamily, 

 though narrow between the maxillipeds, and there is not in this respect the difference 

 that might be expected between Periclimenes and the more stoutly built forms. In 

 Urocaridella and Urocaris, the sterna are narrow, in correspondence with the com- 

 pression of the body. 



The abdomen of the Pontoniinae is of the cai'idean type, with a fairly large 

 first segment, a very large second segment, and a bend between the third and fourth 

 segments. This bend is most marked in Urocaridella and Urocaris, but it is distinct 

 in all other genera except Pontonia, Pontonides, and Conchodytes, where it is merged 

 into a general curvature of the hinder segments. In the more sedentary genera the 

 pleura of the first three segments of the female are very large and foliaceous, and 

 form, with the incurved tail fan, a great pocket for the eggs. In Urocaridella and 

 some species of Urocaris the hinder part of the third tergum is swollen into a hump, 

 and bears a hooked process which overhangs the succeeding segment. 



