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 A HISTORY OF LEICESTERSHIRE will yield the Gammarus, its gardens and roadsides and bosky dells will supply many species of woodlice or woodland shrimps. These are the Isopoda terrestria, sessile-eyed, fourteen-legged, with short carapace, in all these respects agreeing with the Amphipoda, but differing from them by having some appendages of the pleon or tail converted into breathing organs, instead of having gills attached to the legs of the middle-body. Their abundance and extensive range make it really singular that they should for so long have escaped all notice in this county, where hitherto, so far as public records are concerned, the only malacostracan rescued from the realms of conjecture has been Asellus aquaticus, Linn. This, indeed, is our only distinctively fresh- water isopod in England, very abundant, very widely distributed, but not to be regarded as quite a typical isopod, since, of the six pairs of appendages proper to the pleon, the female has lost or dispensed with the second pair. In contrast with the state of inanition in the great sub-class above- mentioned, the Entomostraca are now making their presence known in no inconsiderable variety. The credit of this development is in a large measure due to two investigators, one being the late Mr. Garnar, whose name has already been brought forward, the other, Mr.J. D. Scourfield, whose intimate knowledge of the subject gives exceptional value to the unpublished list of species with which he has generously supplied me. There are, however, as will presently appear, one or two additional authorities to whom the county is indebted for discoveries of special interest. The three orders among which the Entomostraca are distributed, the Branchiopoda, Ostracoda, and Copepoda, are so remarkably unlike in general facies that some study is required before the propriety of classing them side by side can be appreciated. Yet, in spite of this diversity, there are certain forms which have been bandied to and fro between the first and third orders, without obtaining, even to this day, a quite secure position in either. These are the Branchiura, at present by some accepted as a sub-order of the Branchiopoda, sharing that rank with the Phyllopoda and Cladocera. Alter- natively, the three divisions have been raised to independent orders, near to one another. But Mr. Charles Branch Wilson, in his very valuable ' Systematic Review ' of the family Argulidae, 8 would again make them a sub- order of the Copepoda. This is not a fitting opportunity for discussing his arguments. Apart from these his definition of the Branchiura may con- veniently be quoted. According to this they have a ' flattened body, consisting of a shield-shaped cephalothorax in which the first thoracic segment is fused with the head, a free thorax of three segments, and a two-lobed abdomen without segments ; four pairs of swimming feet, long and furnished with two rows of plumose setae ; two large compound eyes, movable, and surrounded by a blood sinus ; testes in the abdomen ; heart present ; females without ovisacs, eggs attached to foreign objects.' There is only one family, including three genera. For instituting a comparison between the Branchiura on the one hand and the malacostracan crayfish or isopods on the other, we may accept the opinion that in the former the paired appendages, apart from the eyes, repre- sent in succession first and second antennae, mandibles, first and second maxillae, maxillipeds, and four pairs of two-branched locomotive limbs, in
 * Proc. U.S. Nat. Mas. xxv, 701 (1902).