MARINE CRUSTACEANS. 683 
Such habits as these need a corresponding habitat, and the Spider-Crabs are essentially 
haunters of weeds, and weed-like animals. The larger kinds cling to the rocks and stones 
on which grow the organisms they clothe themselves with. The walking-legs of such species 
usually end in strong, sharp, 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 even 
sub-chelate claws on the hinder legs with which to cling to the branches, while one or 
both of the second and third pairs are long—probably because they are used in climbing 
(Pl. XLVII. figs. 1, 3 and 4). The first pair (chelipeds) are also sometimes used, monkey- 
wise, in clambering. Research will no doubt show that some of the peculiar features of 
particular species and genera are adaptations to special kinds of sessile organisms. At present 
I can only recall the flat, leaf-like body of Huenia, which resembles the Halimeda-weed 
among which it is generally found (see below, p. 686), and it is certainly the case that 
very many species show no preference whatever in this respect. 
The habit of living on or among sessile organisms is probably kept up by some of 
the members of the other two families of the Oxyrhyncha, although it is the Matidae 
alone which clothe themselves in the way described above. Further information, however, 
is much needed on this point. The Hymenosomidae (Fig. 122) seem clearly adapted by 
their structure—their delicate bodies and slender legs with hooked end-joints—for living on 
plants or zoophytes. They may certainly sometimes be found in such situations, but are 
also reported to have been taken under stones!, a position for which their flat backs are 
not unsuitable. Among the Parthenopidae, the Eumedoninae are probably guests of other 
organisms. Zebrida has, indeed, been taken among the spines of a sea-urchin whose colouring 
it assumes. But the Parthenopinae (Pl. XLVII. fig. 5) have an entirely different habitat. 
The members of this subfamily have left the weed (that they originally had the same 
habits as the Matidae seems likely from the occurrence of hooked hairs, slight and few in 
number, in certain members of the genus ZLambrus) and have taken up the same _ habitat 
as the Oxystomata—that is to say beds of sand and shingle. The result is a series of 
modifications strikingly like some of those which are found in the latter group» The 
overlapping wings of the carapace which hide the legs of Calappa and Tlos reappear in 
such forms as Cryptopodia, Heterocrypta and Oethra and less strongly marked in Lambrus, 
especially L. calappoides. The long chelipeds of some Leucosiids are repeated in an altered 
shape in various species of Lambrus and Parthenope. The bent fingers of Ranina and some 
species of Calappa are found throughout the group. In Lambrus calappoides we find again 
the flat hands of Calappa held against the breast. But the most striking of these likenesses 
is the arrangement of the inward channel for the breathing-stream in Aulacolambrus, which, 
while it is wholly new, yet strongly recalls that of the Leucosiidae. In this subgenus, the 
underside of the carapace (pterygostome) is traversed, on each side, just outside the third 
maxilliped, by a deep groove which is covered in, not like the analogous channel in the 
Leucosiidae by the maxillipeds, but by thick fringes of hairs borne by the maxillipeds and 
by the carapace, becoming thus a closed tube leading from the front of the body to the 
opening of the gill-chamber at the base of the chelipeds (Pl. XLVII. fig. 6). A similar 
1 Adams and White, Crustacea of the Samarang. The ganisms. Or, again, it may be that the hollows under the 
authors make the same statement about Trapezia, which is stones from which the Hlamena was taken were lined, as 
certainly 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 2 See above, pp. 434, 435. 
the neighbourhood of their natural habitat, growing or- 
