VI FAMILIES OF CATOMETOPA 195 



astonishing rapidity, and they seem to be always on the alert, 

 directing their eyes, which are placed on exceedingly long stalks, 

 in all directions. 



Some of the Grapsidae, e.g. Aratus pisonii, are partially 

 adapted for life on land. Fritz Mu'ller, in his Facts for Dar/'-in. 

 alludes to this creature as " a charming lively crab which 

 ascends mangrove bushes and gnaws their leaves." The carapace 

 can be elevated and depressed posteriorly, apparently by means 

 of a membranous sac, which can be inflated by the body-fluids. 

 This Crab retains its gills and can breathe iinder water in the 

 ordinary way. 



A great many other Catometopa are land-crabs ; but we may 

 specially mention the genus Gecarcinvs, related to the marine 

 Grapsidae, which has representatives in the West Indies and 

 West Africa. The Crabs of this genus may live in sheltered 

 situations several miles from the sea, but in spring the whole 

 adult population rushes down in immense troops to the shore, 

 where breeding and spawning take place ; and when this is 

 completed they migrate back again to the laud. The young pass 

 through the normal larval stages in the sea and then migrate 

 inland. 1 



Fam. 1. Carcinoplacidae. The carapace is rounded and 

 broader than long, usually with toothed front margin. The 

 orbits and eyes are normal, and not much enlarged. Geryon, in 

 the deep littoral of the northern hemisphere. Euryplax, Pano- 

 plax, etc., in the American coastal waters. Typhlocarcinus, etc., 

 in the Indo-Pacific. 



Fam. 2. Gonoplacidae. The carapace is square, with the 

 antero-lateral corners produced into spines. The orbits are 

 transversely widened, and the eye-stalks long. Gonoplax, widely 

 distributed in the littoral zone. G. rhomboides in British and 

 European seas. 



Fam. 3. Pinnotheridae. Carapace round, with indistinct 

 frontal margin. Orbits and eyes very small, often rudimentary. 

 The members of this family live symbiotically or parasitic-ally 

 in the shells of living Bivalve Molluscs, corals, and worm- 

 tubes in all seas except the Arctic. Pinnotheres pisum is fairly 



1 There appears to be some doubt on this point, as Westwood (see p. 153) 

 described direct development in a Gecarcinus. Possibly different species behave 

 variously. 



