NATURAL HISTORY. 
81 
ROOM IV.] 
The Crabs (Cases 3 to 19) differ from the Lobsters 
and Prawns in their caudal rings being less developed, 
and bent under the hinder part of the greatly expanded 
thorax. 
Amongst these short-tailed Crustacea are specimens of 
the Swimming Crabs of the genera Portunns , Podoph- 
thalmus , &c. These animals have the posterior leg ter¬ 
minated by very flat joints, of an oval or orbicular form, 
and calculated to act as fins in swimming. The last pair 
of legs in all the Swimming Crabs, is constantly furnished 
with these flattened joints, and in some species the pre¬ 
ceding pairs have them also, but never so broad as those 
of the hind legs. The eyes of the Telescope Crab, ( [Pod- 
vphthalmus spinosus ,) Case 17> are supported on very 
long slender pedicles, reaching from the middle of the an¬ 
terior margin of the shell to the lateral angles, and lodged, 
when at rest, in a groove on the edge: this is the only 
known recent species belonging to this genus. Some of 
the Freshwater Crabs, which live in the rivers and streams, 
and are capable of existing a considerable time out of the 
water; one species, peculiar to the south of Europe and 
the Levant, (Le Cancre de riviere of Rondeletius,) enjoyed 
great celebrity amongst the Greeks, for its supposed 
medicinal virtues, and is frequently represented on the 
coins of Agrigentum with the utmost accuracy. Some 
of the Crabs peculiar to hot countries, which are remark¬ 
able for the rapidity of their motions, and other pecu¬ 
liarities ; they live in holes, usually near the sea-shore 
or in the neighbourhood of water; these holes are of a 
cylindrical form, oblique, and very deep, and several of 
them are generally found near together, but each hole 
contains only one inhabitant. When the animal of one 
of the genera belonging to this family ( Gelasimus ) is 
in its hole, it closes the entrance with its claw, one of 
which, sometimes the right, sometimes the left, is com¬ 
monly much larger than the other. These Crustacea 
have also a singular habit of holding up the large claw 
in front of the body, as if they were beckoning to some 
one at a distance, whence they have acquired the name 
of Calling Crabs (Cancer vocans, Linn.). What has 
been said of the rapidity of the motions of these Crus¬ 
tacea, is particularly applicable to those of the genu? 
e 3 
