Decapoda — Brachyura, Cra 6s. 



65 



The DiiOiMiACKA or Spouge- Crabs are tlie most primitive of the Tablu-case 

 existing Brachyura. The last pair, or the last two pairs, of legs are 

 dorsal in position, with hooked or prehensile claws, and are used 

 for holding a piece of sponge, an Ascidian, or half of a bivalve 

 shell, under which the animal is completely hidden. The mouth- 

 frame is square. The primitive character of the group is shown 

 especially l:)y the retention of a vestigial pair of limbs on the first 

 abdominal somite of the female, and often on the sixth abdominal 



Dnnnia rulgnris. Front view of a specimen canying on its back a mass of the 

 sponge Clionc celata (reduced). [Table-case No. 12. J 



somite in both sexes {sec the exhibited specimen of Dromia laioi'). 

 The basal segment of the antenna is large and unusually free, 

 the pits into which the antennules fold are not separated from the 

 orbits, and the gills are, in most cases, more numerous than in the 

 other Brachyura. The oviducts of the female open on the first 

 segment of the third pair of legs. 



Many of the Dromiacea, especially the more primitive forms, 

 inhabit the deep sea. Dromia vulgaris (Fig. 44), which occurs off 

 the South of England, belongs to the family Dromiidae, in which 

 the last two pairs of legs are generally reduced in size, and are 



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