NATURAL HISTORY. 
153 
ROOM IV.] 
larger species are dreaded in warm climates, and some are phosphores¬ 
cent, as the genera Scutigera, Lithobius , and Scolopendra. 
The Crustacea, Cases 13 to 22, are the only Annulose animals 
with jointed feet that respire by gills; these gills are generally placed 
near the base of the legs, and are protected by the border of the tho¬ 
racic shell, or carapace, but in a few they are external. They are the 
giants among the Annulosa, and all live in the water. Some few leave 
it for a short time in search of food, but they return to it to breed and 
respire. Many kinds are found in a fossil state. 
The more typical Crustacea have their eyes placed on a peduncle 
(Podophthalma ) furnished with a facetted cornea, and the rings of the 
thorax are covered by a common shell. Among these, by far the 
greater number are called Decapodes, because they have five pairs of 
feet, with the gills at their base under the thorax, and five pairs of feet¬ 
like jaws. Their head is covered with the same hard common case as 
the thorax. 
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 Portunus , Podophthalmus, &c. These animals 
have the posterior leg terminated by very flat joints, of an oval or orbi¬ 
cular 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 preceding pairs have them also, 
but never so broad as those of the hind legs. The eyes of the Tele¬ 
scope Crab, {Podophthalmus spinosus, Case 17,) are supported on very 
long slender pedicles, reaching from the middle of the anterior 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, are capable of existing a considerable time out of the water ; 
one species, peculiar to the south of Europe and the Levant, {Le Cart¬ 
er e 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 are remarkable for the rapidity of 
their motions, and other peculiarities ; 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 gene¬ 
rally found near together, but each hole contains only one inhabitant. 
When the animal of one of the genera belonging to this family ( Gelasi- 
rnus) is in its hole, it closes the entrance with its claw, one of which, 
sometimes the right, sometimes the left, is commonly 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 Crustacea, is particularly applicable to those of the 
genus Ocypode , (Case 17,) which hide in holes in the sand on the sea¬ 
shore during the day, and leave them at sunset. The genus Pinnotheres 
is a very small race of Crustacea inhabiting bivalve shells, and supposed 
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