Decap oda — Brachyu ra. 
67 
of water from the gills, and in most other crabs open at the front Table-case 
corners of the mouth-frame, are produced forwards to the front of No> 
the head and are closed in below by plate-like processes from the 
endopodites of the first maxillipeds. This arrangement is cor- 
related with the characteristic habits of the tribe, nearly all the 
members of which conceal themselves in the sand, where they lie 
buried with only the eyes exposed. 
In the family Calappidae the openings by which the water 
enters the gill-chambers are situated, as in most Brachyura, in 
front of the bases of the chelipeds. The legs are normal in 
position. 
A specimen of Calappa hepatica is exhibited which has been 
prepared to illustrate the distinctive characters of the tribe. The 
second and third maxillipeds have been removed on one side to 
show the triangular mouth-frame (coloured red) and the process 
from the endopodite (coloured blue) of the first maxilliped. The 
arrow indicates the course of the respiratory current. A broad 
space (marked X), free from hair, is seen on each side of the 
mouth-frame leading down to the entrance of the gill-chamber. 
When the chelipeds are closed up against the under surface of the 
body, as in one of the specimens of Calappa flammea exhibited, this 
space is converted into a tubular channel, through which a supply 
of pure water can reach the gills when the crab is buried in the 
sand. 
The species of the genus Matuta swim well by means of their 
flattened, paddle-shaped feet, which are also used for digging in 
sand. The animals are said to bury themselves with wonderful 
rapidity. The channel leading to the entrance of the gill-chamber, 
seen in the preparation of Calappa, is here much deepened in its 
front portion, where the overarching hairs convert it into a tubular 
passage opening into the orbit. 
In the family Leucosiidae the channels leading to the gills are 
completely covered in by the expanded exopodites of the third pair 
of maxillipeds. This character is illustrated by a preparation of 
Parilia alcocki (the largest species of the family), in which the 
second and third maxillipeds have been removed on one side. 
The mouth-frame is coloured red and the endopodite of the first 
maxilliped blue. X marks the inhalent respiratory channel. One 
of the third pair of maxillipeds is mounted separately to show the 
greatly expanded exopodite which, in the natural position, covers 
the inhalent channel. 
The only Oxystomata found in British seas are several species 
