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 CRUSTACEANS the crayfish. The species of woodlice in England amount to more than a score. Many of them are so generally distributed that it will be no exaggerated estimate to credit Bedfordshire with half a score of them. Mr. James Saunders assures me that he often meets with them when he is hunting for mycetozoa, and certainly in that or any similar research Philoscia muscorum (Scopoli) could not well fail to be met with. Oniscus asellus, Linn., Porcellio scaber, Latreille, and Armadillidium vu/gare (Latreille) make themselves familiar everywhere. But none, even of these the commonest of the common, appear to have been specially recorded for this county. The two sessile-eyed groups agree in the character of the eyes. They agree in having seven segments of the middle body freely movable, and not as in the Decapoda covered by the carapace. They agree also to a great extent in the distribution of their appendages, for they follow up the two pairs of antenna?, not by six pairs of jaws and five pairs of trunk-legs, but by four pairs of jaws and seven pairs of trunk-legs. But these features of agreement do not exclude strongly-marked differences. The Isopoda, whether terrestrial or aquatic, being usually flattened from above downward, are fitted for walking ; whereas the Amphipoda, being as a rule laterally compressed, in clumsy attempts at an upright gait commonly fall over on one side and have to slidder. A more important distinction depends on the position of the breathing organs. These in the Amphipoda are sacs or vesicles, simple or pleated or twisted, attached to some or all of the trunk-legs except the first pair. In the Isopoda they are not in the trunk or middle body at all, but in the tail part, otherwise known as abdomen or pleon. Some of the appendages of this pleon, the thin-skinned flattened pleopods, are respiratory. The equi- valent appendages in the pleon of the Amphipoda have no such function, although they may be considered in some measure auxiliaries to it. That the Amphipoda are represented in Bedfordshire does not rest upon conjecture, for early in February, 1902, Mr. James Saunders very oblig- ingly collected from the river Lea near Luton some specimens which he packed in damp moss and dispatched by post. They reached me the following day, languid but still alive, and proved to be, as Mr. Saunders supposed, the wide-ranging Gammarus pulex (Linn.). This may be taken as a typical representative of the Amphipoda at large, but especially of the Gammaridea, the most extensive of the three sections into which the whole group has been divided. Just as nature has been at the pains to distribute Asellus aquaticus (Linn.) over all parts of England as if with intent to provide a type of water-breathing isopods, so has Gammarus pulex in the companion group been made everywhere available. At all events no English naturalist can excuse an utter ignorance of sessile-eyed Crustacea on plea or pretence that specimens are not procurable for investigation. The beginner will soon find his wits well exercised if he attempts to compare the common freshwater gammarus with two other species that are common on the seashore, namely G. locusta and G. marinus. He might at first impatiently refuse to believe that the three species 93