80 A HISTORY OF RECENT CRUSTACEA 
In the last four genera it will be perceived that the 
maxillipeds do not form a complete operculum, but by the 
arrangement of the inner edges of their third and fourth 
joints they leave a lozenge-shaped space over the mouth- 
opening uncovered, while in Uca and Gecarcinucus the 
straight inner edges from either side can be brought exactiy 
together so as to close the cavity completely. Mr. Wood- 
Mason points out that the character of the exopod distin- 
guishes Gecarcinus, Gecarcoidea (which he calls Pelocar- 
cinus), and Hylceocarcinus from the three preceding genera, 
and that they are distinguished from one another by a 
further character of the maxillipeds, for in Gecarcinus the 
three terminal joints are completely hidden, in Hyleocar- 
cinus they are partially visible, and in Gecarcoidea com- 
pletely so. 
None of the Crustacea have more attracted the atten- 
tion and excited the wonder of travellers than some of 
those belonging to this group. Like the twin snakes that 
came over the sea and deliberately landed at Troy to slay 
Laocoon and his two sons, these crabs have, contrary to 
nature, forsaken the ample waters of the ocean, scorned 
all the brooks and rivers and lakes, and carried out a 
portentous invasion of the dry land. Still they are by no 
means indifferent to moisture. The vaulted part of the 
carapace over the branchial regions is lined with a very 
spongy membrane, and sometimes a fold of the membrane 
along the lower edge of the cavity forms a kind of tube in 
which water may be held as in a reservoir. But their 
form and structure are not so surprising as their manners 
and customs. 
Under the heading Cancer ruricola, a species of Gecar= 
cinus, Herbst brings together many curious particulars, 
depending largely upon Patrick Browne’s ‘History of 
Jamaica. In the Bahamas, he says, and in tropical 
regions these land-crabs are so numerous that when they 
creep out of their holes the ground seems to be in motion. 
One litile island is so full of them that it has been called 
Crab Island. They are just as frequent in certain districts 
of Jamaica and in some of the Caribbee islands. The same 
