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MARINE CRUSTACEANS. 683Such habits as these need a corresponding habitat, and the Spider-Crabs are essentiallyhaunters of weeds, and weed-like animals. The larger kinds cling to the rocks and stoneson which grow the organisms they clothe themselves with. The walking-legs of such speciesusually end in strong, shai-p, curved claws by which they can hold fast to the ground.Smaller kinds often live on the weed itself, and these frequently bear hooked or evensub-chelate claws on the hinder legs with which to cling to the branches, while one orboth of the second and third pairs are long — probably because they are used in climbing(PI. XLVII. figs. 1, 3 and 4). The first pair (^chelipeds) are also sometimes used, monkeywise,in clambering. Research will no doubt show that some of the peculiar features ofparticular species and genera are adaptations to special kinds of sessile organisms. At presentI can only recall the flat, leaf-like body of Huenia, which resembles the Haliiueda-weedamong which it is generally found (see below, p. 686), and it is certainly the case thatvery many species show no preference whatever in this respect.The habit of living on or among sessile organisms is probably kept up by some ofthe members of the other two families of the Oxyrhyncha, although it is the Maiidaealone which clothe themselves in the way described above. Further information, however,is much needed on this point. The Hymenosomidae (Fig. 122) seem clearly adapted bytheir structure—their delicate bodies and slender legs with hooked end-joints—for living onplants or zoophytes. They may certainly sometimes be found in such situations, but arealso reported to have been taken under stones', a position for which their flat backs arenot unsuitable. Among the Parthenopidae, the Eumedoninae are probably guests of otherorganisms. Zehrida has, indeed, been taken among the spines of a sea-urchin whose colouringit assumes. But the Parthenopinae (PI. XLVII. fig. 5) have an entirely different habitat.The members of this subfamily have left the weed (that they originally had the samehabits as the Maiidae seems likely from the occurrence of hooked hairs, slight and few innumber, in certain members of the genus Lamhrus) and have taken up the same habitatas the Oxystomata—that is to say beds of sand and shingle. The result is a series ofmodifications strikingly like some of those which are found in the latter group-. Theoverlapping wings of the carapace which hide the legs of Calappa and Tlos reappear insuch forms as Cryptopodia, Heterocrypta and Oethra and less strongly marked in Larahrus,especially L. calappoides. The long chelipeds of some Leucosiids are repeated in an alteredshape in various species of Lamhrus and Parthenope. The bent fingers of Ranina and somespecies of Calappa are found throughout the group. In Lamhrus calappoides we find againthe flat hands of Calappa held against the breast. But the most striking of these likenessesis the arrangement of the inward channel for the breathing-stream in Aulacolamhrus, which,while it is wholly new, yet strongly recalls that of the Leucosiidae. In this subgenus, theunderside of the carapace (pterygostome) is traversed, on each side, just outside the thirdmaxilliped, by a deep groove which is covered in, not like the analogous channel in theLeucosiidae by the maxillipeds, but by thick fringes of hairs borne by the maxillipeds andby the carapace, becoming thus a closed tube leading from the front of the body to theopening of the gill-chamber at the base of the chelipeds (PI. XLVII. fig. 6). A similar1 Adams and White, Crustacea of the Samarang. The ganisms. Or, again, it may be that the hollows under theanthors make the same statement about Trapezia, which is stones from which the Elamena was taken were lined ascertainly a coral crab. Perhaps these genera take shelter such hollows often are, with a scrubby growth of weed.under stones when they are by some accident removed from - See above, pp. i'6i, 435.the neighbourhood of their natural habitat, growing or-