60 DK. G. C. BOURNE ON THE HANINID^ : 
first three pairs ol: pereiopods, the fourtli pair being used to shovel Ihe dis- 
placed sand outwards. When dug in, the animal may be inferred to assume 
an oblique position, the frontal spines of the carapace just breaking the 
surface of tlie sand ; the chelipeds are folded up under the pterygostomial 
region of the carajjace and the long three-jointed eye-stalks may be extended 
well above the sand on the look-out or, on the approach of danger, may 
be folded back and concealed in the orbital cavities. In this position the 
normal respiratory current will be provided for by the rakjng action of 
the chelipeds and the lateral water- passages enclosed between the 
pereiopods and the thoracic epimera, as described above. These afford a 
mechanism whereby filtered water is supplied to the posterior branched 
openings, and the normal exhalant current wiir pass out by the narrow 
anterior passage bounded below by the merus of the third maxilliped and 
lateralljr by the flattened basal joints of the second antennae. 
As the Raninidsc are tropical and sub-tropical crabs living at considerable 
depths it has not been possible for me to observe the habits of the living- 
animals, much less to make experiments on their respiratory mechanisms. 
But in the absence of direct evidence I consider myself justified in giving 
the foregoing account of the course of the normal respiratory current, the 
more so because an examination of numerous specimens of Notopoides latiis 
and of several examples of Zanclifer caribensis in the British Museum of 
Natural History gives the clearest evidence that these species are sand 
burrowers, and that an inhalant current passes into their branchial chambers 
through the posterior branchial orifices, which are exceptionally large and 
conspicuous in these cases. In nearly all the individuals of these two species 
the conspicuous hairy fringes of the pereiopods, of the abdominal pleura, of 
the edges of the branchiostegite, and of the epaulettes of the eleventh sterna, 
are more or less heavily clogged with sand, a fact which bears witness to 
their function as a filtering ap[)aratus. On the other hand, the water- 
passages lying between the posterior thoracic epimera and the pereiopods, 
and therefore guarded by these hairy fringes, are remarkably clean and free 
from sand. The filtration, however, has not been perfect, for the walls of 
the posterior branchial passages are encrusted with fine particles of sand, 
the distribution of which leaves no doubt that the current which deposited 
them set in from behind forwards. The evidence in these two species is 
remarkably clear, and the inferences drawn from it may be extended to 
Notopus dorsipes and to Notoscdes chimmonis, though, in the last-named 
species, in which the last pair of pereiopods are great!)' reduced in size, there 
is evidence that the posterior inhalant respiratory current is becoming of less 
importance and that the incurrent supply of water to the branchial chamber 
is chiefly provided for by special modifications of the antennary region. 
In the absence of opportunities for observation of and experiment on living 
