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 A HISTORY OF HERTFORDSHIRE known for the whole of Great Britain and Ireland, only reaches the number of twenty. Of these one is found in Ireland and has not hitherto been found in England, while five have been found in England which have not yet been discovered in Ireland. Two of the twenty species are not to be expected at any great distance from the coast, and a third is perhaps only a recent importation into our island, an immi- grant from the continent. Of the ten species found in the Berkhamsted garden one was an addition not merely to the fauna of the county but to the fauna of the country, completing the score of which the United Kingdom can boast. The Oniscoidea, or terrestrial isopods, best known among us by the name of woodlice, and in French as cloportides or door-nails, are divided into four principal families the Ligiida?, Trichoniscidae, Oniscidae, and Armadillidiidas. These are separated by numerous differences, and united by numerous points of agreement. All in common have sessile eyes, unless they happen to be blind. All in common have seven pairs of trunk-legs, though as a rule they quit the egg with the seventh pair un- developed or ineffective. All in common have the breathing apparatus not connected with the head or trunk, but pertaining to the appendages of the pleon or tail part, the branchial structure being sometimes modi- fied the better to suit atmospheric respiration. In all these respects they differ strikingly from the crayfish, though equally with it belonging to the Malacostraca. With the first of the four families, the maritime or coast-loving Ligiida?, we are not here concerned. The other three fami- lies are represented in Hertfordshire by nine genera, including the ten species already referred to, on which some brief notes may be offered. The first three species to be mentioned belong to the family Trichonis- cidas. Trichoniscus roseus (Koch) has been described under two other generic names, Itea and Pbilougria, the latter meaning a lover of damp, which would be a fairly appropriate designation for almost all the iso- pods that ever existed. The specific name roseus refers to a character which the inexperienced would little expect to find, and which is in fact very rare, in a woodlouse, namely the beautifully delicate rose-tint of its colouring. Many species display bright colours and highly effective patterns, while some are modestly dressed in white or creamy hues, and others in sober greys and browns. But no other species is at once so beautiful and so unobtrusive as the little Tricboniscus roseus. Its distribution is widely extended. It is very agile, like many others of its family. It may not have a feeling for poetry, but by all its manoeuvres to escape observation it shows plainly that, if ' many a rose is born to blush un- seen,' such is the privacy it earnestly desires for itself. Tricboniscus pusillus, Brandt, is a still smaller species, which has passed under the same series of generic names and also under three specific names other than that which is proper to it, one of these syno- nyms being ce/er, in allusion to the great celerity of its movements, by which it is quite capable of foiling the efforts of a pursuer who is 184