Decapoda — Bracliyu ra. G 7 



of water from the fiills, and in most other crabs open at the front Table-case 

 corners of the mouth-frame, arc produced forwanls to the front of •^"- ■'■'^• 

 the liead and are closed in l)elo\v by plate-Hko processes from the 

 endopodites of the first maxihipeds. Tliis arrangement is cor- 

 related with the characteristic habits of the tribe, nearly all the 

 members of which conceal themselves in the sand, where they He 

 buried with only the eyes exposed. 



In the family Calappidac the opening's l)y 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 Calajtpct hepatica is exhibited which has been 

 prepared to illustrate the distinctive ciiaracters of the tribe. The 

 second and third maxillipeds liave been removed on one side to 

 show the triangular moutli-frame (coloured red) and the process 

 from the endopodite (coloured blue) of the first maxilliped. The 

 arrow indicates the course of the respiratory current. \ 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 



F 2 



