258 HISTORY OF BRITISH CRUSTACEA. 
Division ENTOMOSTRACA * 
Aquatic Crustacea covered with a shell of a horny or 
leathery substance, formed of one or more pieces, in some 
resembling a bivalve shell, in others a buckler which either 
entirely or in part envelopes the body and the limbs of the 
animal ; branchiae attached to the feet or jaws ; feet jointed 
and fringed with hairs. They undergo a regular moulting 
or change of shell, in some amounting to a species of trans- 
formation. 
Legion BRANCHIOPODA, 
Mouth with organs adapted for mastication; branchiae 
many, attached to the feet ; body sometimes naked, but 
most usually with a buckler-like envelope, in some enclosing 
only the head and thorax, in others the whole body ; feet 
all bearing branchiae; antennae two or four, jointed, and 
generally ciliated ; eyes sometimes two or three, but often 
only one, or so close to each other as to appear single. The 
species are all free, swimming at large in the water. 
* E vTOjuos, an insect ; o(TrpaKoy } a shell. 
