DECAPODA. BRACHYURA. 547 



They burrow between tide marks, and, as the name implies, are very swift 

 of foot. Running on tip-toe, with the long eye-stalks erect, " on wind- 

 swept stretches of sandy beach, and coloured like the sand, they sometimes 

 seem rather to be borne on the wings of the wind than to run " (Stebbing). 

 They take air into the branchial cavity, and are unable to survive a pro- 

 longed immersion in water (Fr. Muller) ; afferent orifice between the 

 bases of 4th and 5th walking legs, guarded by fringes of hairs. Gelasimus 

 Latr. One of the chelae (r. or 1.) very large in the male. They live, in 

 pairs, in burrows, on sandy shores in the tropics, often in great numbers, 

 and between tides come out and feed. The great chela of the male is 

 brightly and variously coloured, giving the stretches of sand they frequent 

 the appearance of being strewn with coloured beans. It is held aloft and 

 brandished, in defiance, at the neighbouring males, who simultaneously 

 respond with a similar motion. Sometimes an engagement occurs, the- 

 males grasping hands. If they are disturbed there is a flash of the great 

 chelae as the crabs retreat to their burrows and in a moment the shore is: 

 deserted. They live on vegetable matter in the sand, and (in Tongatabu) 

 are eaten by king-fishers. Gonoplax Leach, chelipeds very long in male ; 

 G. rhomboides (L.) British ; many other genera. In Macrophthalmus 

 Latr., Helice de Haan, and Metaplax M. Edw. the males are provided with 

 stridulating apparatus. Bathyplax A. M. Edw. B. typhlits A. M. Edw. 

 Specimens from 4-500 fathoms blind, while those from shallow water 

 can see. 



Fam. 3. Gecarcinidae. Land crabs. Carapace dorsally convex, 

 dilated over the branchial regions, anterolateral margins entire ; front of 

 moderate width ; terminal joint of walking legs armed with spines ; 

 Branchial chambers lined by spongy membrane, and only partially occu- 

 pied by the gills. A supply of water is retained in them. Uca Leach, 

 and Gecarcinucus M. Edw. 3rd maxillipeds meet in the middle line. 

 Uca una (L.) in mangrove swamps, Brazil. In Cardisoma Latr., Gecarcoidea 

 M. Edw., Gecarcinus Leach and Hylaeocarcinus Wood-Mason, a lozenge- 

 shaped space is left between these maxillipeds. A species of Gecarcinus 

 inhabits the forests of the W. India Islands, sheltering in holes. In 

 May they make their way in compact bodies, scaling the obstacles in 

 their paths, to the sea, where the eggs are laid. " The noise of their 

 march is compared to the rattling of the armour of a regiment." The 

 young are hatched, according to Westwood, with the form of the adult. 

 This is probably not the case in G. lagostoma, whose wide distribution 

 would suggest that the larva leads a pelagic existence. 



Fam. 4. Pinnotheridae. Carapace more or less membranous, antero- 

 lateral margins entire or nearly so ; eyes very small. Small crabs, many 

 of them living symbiotically with Lamellibranchs, Echini, etc. A crab 

 associated with a Pinna appears on the Egyptian monuments. Pinno- 

 theres, Latr., only 3 pairs of gills. P. veterum Bosc. and P. pisum (L.) are 

 common European (British). The female of the latter is never found 

 outside a host, and the carapace is much more membranous than in the 

 male. Hymenosoma Desmarest ; Scopimera de Haan ; Dotilla Stimpson ; 

 Pinnixa White, 5th legs often short ; Amorphopus Bell, 5th legs rudi- 

 mentary ; Hexapus de Haan, and Thaumastoplax Miers, 5th legs absent. 



Here are probably allied the crabs which live in holes in Corals. In the 

 male the abdomen has the usual shape, but in the female it is large and 

 membranous, with expanded pleura, forming a deep pocket for the re- 

 ception of the eggs. Cryptochirus Heller ; Hapalocarcinus Stimpson. 



