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, ey. Aratus pisonii, are partially 
adapted for life on land. Fritz Miiller, in his Facts for Darwin, 
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 under water in the 
ordinary way. 
A great many other Catometopa are land-crabs; but we may 
specially mention the genus Gecarcinus, 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 land. The young pass 
through the normal larval stages in the sea and then miegrate 
inland.’ 
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. Luryplax, Pano- 
plax, etc., in the American coastal waters.  Zyphlocarcinus, ete., 
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 lone. 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 parasitically 
in the shells of ving Bivalve Molluscs, corals, and worm- 
tubes in all seas except the Arctic. Pinnotheres pisum is fairly 
Oo 
tap) 
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. 
