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 



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