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 A HISTORY OF BERKSHIRE pair frequently offer very serviceable marks of distinction. These appendages consist generally of a five-jointed peduncle and a terminal part called the flagellum. Of the seven species above mentioned the first three have this flagellum at least triarticulate, but in the remaining four it is only biarticulate. In Trichoniscus pusillus the antennae are dis- tinguished by being more spiny and more strongly geniculate than those of other species. In Platyarthrus hoffmannseggii the antennas are broad and flattened, and the first joint of the flagellum is scarcely visible. Where the antenna? fail, other parts supply distinctive characters. Thus in Philoscia muscorum the pleon is more abruptly contracted than in Oniscus asellus. The smooth Metoponorthus pruinosus, as its generic name implies, has a straight forehead, whereas the roughly tuberculate Porcellio scaber has a very prominent rounded lobe on each side of its front. Armadillldium vu/gare is easily known from the others because on slight provocation it rolls itself up into a ball. Should other species be found in the county, as will doubtless be the case, more details will be required for even a rough discrimination of the extended series. Sometimes the eye may be beguiled into expecting a new species when exact examina- tion shows that there is nothing more than variety of colouring. This happens especially in the genera Armadillidium and Porcellio. The prevalent colour of P. scaber is a gloomy black, but there are brightly margined and marbled varieties, which the student must beware of con- fusing with the closely related species P. pictus. The Entomostraca of the county appear to have suffered a neglect which is almost absolute. Dr. Hamilton allows the riverside naturalist to remain serenely unconscious of their existence. Miss Pollard, in lecturing at Reading on ' Animal Parasites,' takes her illustrations from marine species in preference to relying on the remarkable Copepoda which infest our freshwater fishes, or on Argulus fo/iaceus, the widely distributed representative of the Branchiura, which assails carp and sticklebacks, salmon and tadpoles. Miss Green tantalizes expectation by mentioning Cyclops, a genus of the Copepoda, the ostracode genus Cypris, and Daphnia, which may be regarded as the best known genus of all the Cladocera. But, so far as the reports of these lectures inform us, no single species is identified as living in river or rivulet, pond or pool, within the borders of Berkshire. The only actual record that can be relied on is a new one, kindly supplied me by Mr. D. J. Scourfield, editor of the Journal of the Quekett Microscopical Club. He informs me that he took Simocephalus vetulus at Maidenhead on May 20, 1899, and adds, ' I only happened to record this because I found some specimens of the rare males.' In the family Daphniidas, Simocephalus was separated by Schcedler in 1858 from O. F. Muller's genus Dapbnia, a leading distinc- tion between them being that in the elder genus the head is carinate above, while in the newer one, as implied by the generic name signifying ' blunt-head,' it is convex and not carinate. Some divergence of opinion has arisen as to the true name of the species with which we are here concerned. Miiller named a form Daphne vefu/a in 1776. Then in 130